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c.html.markdown
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c.html.markdown
@ -1,11 +1,9 @@
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---
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- name: c
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- category: language
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- language: c
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- filename: learnc.c
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- contributors:
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- [Adam Bard](http://adambard.com/)
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- [Árpád Goretity](http://twitter.com/H2CO3_iOS)
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language: c
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filename: learnc.c
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contributors:
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- ["Adam Bard", "http://adambard.com/"]
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- ["Árpád Goretity", "http://twitter.com/H2CO3_iOS"]
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---
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@ -27,17 +25,10 @@ Multi-line comments look like this. They work in C89 as well.
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#include <stdio.h>
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#include <string.h>
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// file names between <angle brackets> are headers from the C standard library.
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// They are searched for by the preprocessor in the system include paths
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// (usually /usr/lib on Unices, can be controlled with the -I<dir> option if you are using GCC or clang.)
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// (File names between <angle brackets> are headers from the C standard library.)
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// For your own headers, use double quotes instead of angle brackets:
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#include "my_header.h"
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// The C preprocessor introduces an almost fully-featured macro language. It's useful, but
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// it can be confusing (and what's even worse, it can be misused). Read the
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// Wikipedia article on the C preprocessor for further information:
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// http://en.wikipedia.org/wiki/C_preprocessor
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// Declare function signatures in advance in a .h file, or at the top of
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// your .c file.
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void function_1();
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@ -50,132 +41,117 @@ int main() {
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// %d is an integer, \n is a newline
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printf("%d\n", 0); // => Prints 0
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// All statements must end with a semicolon
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///////////////////////////////////////
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// Types
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///////////////////////////////////////
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// You have to declare variables before using them. A variable declaration
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// requires you to specify its type; a variable's type determines its size
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// in bytes.
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// ints are usually 4 bytes
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int x_int = 0;
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// shorts are usually 2 bytes
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short x_short = 0;
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// chars are guaranteed to be 1 byte
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char x_char = 0;
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char y_char = 'y'; // Char literals are quoted with ''
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// longs are often 4 to 8 bytes; long longs are guaranteed to be at least
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// 64 bits
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long x_long = 0;
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long long x_long_long = 0;
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// floats are usually 32-bit floating point numbers
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float x_float = 0.0;
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// doubles are usually 64-bit floating-point numbers
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double x_double = 0.0;
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// Integral types may be unsigned. This means they can't be negative, but
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// the maximum value of an unsigned variable is greater than the maximum
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// signed value of the same size.
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unsigned char ux_char;
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// Integral types may be unsigned.
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unsigned short ux_short;
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unsigned int ux_int;
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unsigned long long ux_long_long;
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// Other than char, which is always 1 byte (but not necessarily 8 bits!),
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// these types vary in size depending on your machine and compiler.
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// sizeof(T) gives you the size of a variable with type T in
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// bytes so you can express the size of these types in a portable way.
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// sizeof(obj) yields the size of an actual expression (variable, literal, etc.).
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// For example,
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// sizeof(T) gives you the size of a variable with type T in bytes
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// sizeof(obj) yields the size of the expression (variable, literal, etc.).
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printf("%zu\n", sizeof(int)); // => 4 (on most machines with 4-byte words)
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// It's worth noting that if the argument of the `sizeof` operator is not a type but an expression,
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// then its argument is not evaluated except VLAs (see below). Also, `sizeof()` is an operator, not a function,
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// furthermore, the value it yields is a compile-time constant (except when used on VLAs, again.)
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// If the argument of the `sizeof` operator an expression, then its argument
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// is not evaluated (except VLAs (see below)).
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// The value it yields in this case is a compile-time constant.
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int a = 1;
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size_t size = sizeof(a++); // a++ is not evaluated
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printf("sizeof(a++) = %zu where a = %d\n", size, a);
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// the above code prints "sizeof(a++) = 4 where a = 1" (on a usual 32-bit architecture)
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// prints "sizeof(a++) = 4 where a = 1" (on a 32-bit architecture)
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// Arrays must be initialized with a concrete size.
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char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
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int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
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// (assuming 4-byte words)
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// You can initialize an array to 0 thusly:
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char my_array[20] = {0};
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// Indexing an array is like other languages -- or,
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// rather, other languages are like C
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my_array[0]; // => 0
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// Arrays are mutable; it's just memory!
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my_array[1] = 2;
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printf("%d\n", my_array[1]); // => 2
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// In C99 (and as an optional feature in C11), variable-length arrays (VLAs) can be declared as well.
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// The size of such an array need not be a compile time constant:
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// In C99 (and as an optional feature in C11), variable-length arrays (VLAs)
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// can be declared as well. The size of such an array need not be a compile
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// time constant:
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printf("Enter the array size: "); // ask the user for an array size
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char buf[0x100];
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fgets(buf, sizeof buf, stdin);
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size_t size = strtoul(buf, NULL, 10); // strtoul parses a string to an unsigned integer
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// strtoul parses a string to an unsigned integer
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size_t size = strtoul(buf, NULL, 10);
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int var_length_array[size]; // declare the VLA
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printf("sizeof array = %zu\n", sizeof var_length_array);
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// A possible outcome of this program may be:
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Enter the array size: 10
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sizeof array = 40
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// > Enter the array size: 10
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// > sizeof array = 40
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// Strings are just arrays of chars terminated by a NUL (0x00) byte,
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// represented in strings as the special character '\0'.
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// (We don't have to include the NUL byte in string literals; the compiler
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// inserts it at the end of the array for us.)
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char a_string[20] = "This is a string";
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printf("%s\n", a_string); // %s formats a string
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/*
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You may have noticed that a_string is only 16 chars long.
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Char #17 is the NUL byte.
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Chars #18, 19 and 20 are 0 as well - if an initializer list (in this case, the string literal)
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has less elements than the array it is initializing, then excess array elements are implicitly
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initialized to zero. This is why int ar[10] = { 0 } works as expected intuitively.
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*/
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printf("%d\n", a_string[16]); // => 0
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// So string literals are strings enclosed within double quotes, but if we have characters
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// between single quotes, that's a character literal.
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// i.e., byte #17 is 0 (as are 18, 19, and 20)
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// If we have characters between single quotes, that's a character literal.
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// It's of type `int`, and *not* `char` (for historical reasons).
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int cha = 'a'; // fine
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char chb = 'a'; // fine too (implicit conversion from int to char - truncation)
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char chb = 'a'; // fine too (implicit conversion from int to char)
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///////////////////////////////////////
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// Operators
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///////////////////////////////////////
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int i1 = 1, i2 = 2; // Shorthand for multiple declaration
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float f1 = 1.0, f2 = 2.0;
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// Arithmetic is straightforward
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i1 + i2; // => 3
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i2 - i1; // => 1
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i2 * i1; // => 2
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i1 / i2; // => 0 (0.5, but truncated towards 0)
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f1 / f2; // => 0.5, plus or minus epsilon - floating-point numbers and calculations are not exact
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f1 / f2; // => 0.5, plus or minus epsilon
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// Floating-point numbers and calculations are not exact
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// Modulo is there as well
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11 % 3; // => 2
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// Comparison operators are probably familiar, but
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// there is no boolean type in c. We use ints instead.
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// (Or _Bool or bool in C99.)
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@ -187,14 +163,14 @@ int main() {
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3 < 2; // => 0
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2 <= 2; // => 1
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2 >= 2; // => 1
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// C is not Python - comparisons don't chain.
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int a = 1;
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// WRONG:
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int between_0_and_2 = 0 < a < 2;
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// Correct:
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int between_0_and_2 = 0 < a && a < 2;
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// Logic works on ints
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!3; // => 0 (Logical not)
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!0; // => 1
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@ -202,7 +178,7 @@ int main() {
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0 && 1; // => 0
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0 || 1; // => 1 (Logical or)
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0 || 0; // => 0
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// Bitwise operators!
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~0x0F; // => 0xF0 (bitwise negation, "1's complement")
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0x0F & 0xF0; // => 0x00 (bitwise AND)
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@ -210,17 +186,17 @@ int main() {
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0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
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0x01 << 1; // => 0x02 (bitwise left shift (by 1))
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0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
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// Be careful when shifting signed integers - the following are all undefined behavior:
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// Be careful when shifting signed integers - the following are undefined:
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// - shifting into the sign bit of a signed integer (int a = 1 << 32)
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// - left-shifting a negative number (int a = -1 << 2)
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// - shifting by an offset which is more than or equal to the width of the type of the LHS:
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// - shifting by an offset which is >= the width of the type of the LHS:
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// int a = 1 << 32; // UB if int is 32 bits wide
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///////////////////////////////////////
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// Control Structures
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///////////////////////////////////////
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if (0) {
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printf("I am never run\n");
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} else if (0) {
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@ -228,36 +204,38 @@ int main() {
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} else {
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printf("I print\n");
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}
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// While loops exist
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int ii = 0;
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while (ii < 10) {
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printf("%d, ", ii++); // ii++ increments ii in-place, after yielding its value ("postincrement").
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printf("%d, ", ii++); // ii++ increments ii in-place
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// after yielding its value ("postincrement").
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} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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printf("\n");
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int kk = 0;
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do {
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printf("%d, ", kk);
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} while (++kk < 10); // ++kk increments kk in-place, and yields the already incremented value ("preincrement")
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} while (++kk < 10); // ++kk increments kk in-place, and yields
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// the already incremented value ("preincrement")
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// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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printf("\n");
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// For loops too
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int jj;
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for (jj=0; jj < 10; jj++) {
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printf("%d, ", jj);
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} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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printf("\n");
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// branching with multiple choices: switch()
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switch (some_integral_expression) {
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case 0: // labels need to be integral *constant* epxressions
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do_stuff();
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break; // if you don't break, control flow falls over labels - you usually don't want that.
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break; // if you don't break, control flow falls over labels
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case 1:
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do_something_else();
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break;
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@ -267,73 +245,74 @@ int main() {
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exit(-1);
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break;
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}
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///////////////////////////////////////
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// Typecasting
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///////////////////////////////////////
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// Every value in C has a type, but you can cast one value into another type
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// if you want (with some constraints).
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int x_hex = 0x01; // You can assign vars with hex literals
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// Casting between types will attempt to preserve their numeric values
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printf("%d\n", x_hex); // => Prints 1
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printf("%d\n", (short) x_hex); // => Prints 1
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printf("%d\n", (char) x_hex); // => Prints 1
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// Types will overflow without warning
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printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long)
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// printf("%d\n", (unsigned char) 257); would be undefined behavior - `char' is usually signed
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// on most modern systems, and signed integer overflow invokes UB.
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// Also, for determining the maximal value of a `char`, a `signed char` and an `unisigned char`,
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|
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// For determining the max value of a `char`, a `signed char` and an `unisigned char`,
|
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// respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h>
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|
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|
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// Integral types can be cast to floating-point types, and vice-versa.
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printf("%f\n", (float)100); // %f formats a float
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printf("%lf\n", (double)100); // %lf formats a double
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printf("%d\n", (char)100.0);
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///////////////////////////////////////
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// Pointers
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///////////////////////////////////////
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// A pointer is a variable declared to store a memory address. Its declaration will
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// also tell you the type of data it points to. You can retrieve the memory address
|
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// of your variables, then mess with them.
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|
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|
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int x = 0;
|
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printf("%p\n", (void *)&x); // Use & to retrieve the address of a variable
|
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// (%p formats an object pointer of type void *)
|
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// => Prints some address in memory;
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|
||||
|
||||
|
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|
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// Pointers start with * in their declaration
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int *px, not_a_pointer; // px is a pointer to an int
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px = &x; // Stores the address of x in px
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printf("%p\n", (void *)px); // => Prints some address in memory
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printf("%zu, %zu\n", sizeof(px), sizeof(not_a_pointer));
|
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// => Prints "8, 4" on a typical 64-bit system
|
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|
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|
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// To retreive the value at the address a pointer is pointing to,
|
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// put * in front to de-reference it.
|
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// Note: yes, it may be confusing that '*' is used for _both_ declaring a pointer and dereferencing it.
|
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printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of
|
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|
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// Note: yes, it may be confusing that '*' is used for _both_ declaring a
|
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// pointer and dereferencing it.
|
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printf("%d\n", *px); // => Prints 0, the value of x
|
||||
|
||||
// You can also change the value the pointer is pointing to.
|
||||
// We'll have to wrap the de-reference in parenthesis because
|
||||
// ++ has a higher precedence than *.
|
||||
(*px)++; // Increment the value px is pointing to by 1
|
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printf("%d\n", *px); // => Prints 1
|
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printf("%d\n", x); // => Prints 1
|
||||
|
||||
int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory
|
||||
|
||||
// Arrays are a good way to allocate a contiguous block of memory
|
||||
int x_array[20];
|
||||
int xx;
|
||||
for (xx = 0; xx < 20; xx++) {
|
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x_array[xx] = 20 - xx;
|
||||
} // Initialize x_array to 20, 19, 18,... 2, 1
|
||||
|
||||
|
||||
// Declare a pointer of type int and initialize it to point to x_array
|
||||
int* x_ptr = x_array;
|
||||
// x_ptr now points to the first element in the array (the integer 20).
|
||||
@ -342,50 +321,52 @@ int main() {
|
||||
// it decays into (implicitly converted to) a pointer.
|
||||
// Exceptions: when the array is the argument of the `&` (address-od) operator:
|
||||
int arr[10];
|
||||
int (*ptr_to_arr)[10] = &arr; // &arr is NOT of type `int *`! It's of type "pointer to array" (of ten `int`s).
|
||||
int (*ptr_to_arr)[10] = &arr; // &arr is NOT of type `int *`!
|
||||
// It's of type "pointer to array" (of ten `int`s).
|
||||
// or when the array is a string literal used for initializing a char array:
|
||||
char arr[] = "foobarbazquirk";
|
||||
// or when it's the argument of the `sizeof` or `alignof` operator:
|
||||
int arr[10];
|
||||
int *ptr = arr; // equivalent with int *ptr = &arr[0];
|
||||
printf("%zu %zu\n", sizeof arr, sizeof ptr); // probably prints "40, 4" or "40, 8"
|
||||
|
||||
|
||||
|
||||
// Pointers are incremented and decremented based on their type
|
||||
// (this is called pointer arithmetic)
|
||||
printf("%d\n", *(x_ptr + 1)); // => Prints 19
|
||||
printf("%d\n", x_array[1]); // => Prints 19
|
||||
|
||||
|
||||
// You can also dynamically allocate contiguous blocks of memory with the
|
||||
// standard library function malloc, which takes one argument of type size_t
|
||||
// representing the number of bytes to allocate (usually from the heap, although this
|
||||
// may not be true on e. g. embedded systems - the C standard says nothing about it).
|
||||
int *my_ptr = malloc(sizeof(*my_ptr) * 20);
|
||||
for (xx = 0; xx < 20; xx++) {
|
||||
*(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here, and it's also more readable
|
||||
*(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx
|
||||
} // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
|
||||
|
||||
|
||||
// Dereferencing memory that you haven't allocated gives
|
||||
// "unpredictable results" - the program is said to invoke "undefined behavior"
|
||||
printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? It may even crash.
|
||||
|
||||
|
||||
// When you're done with a malloc'd block of memory, you need to free it,
|
||||
// or else no one else can use it until your program terminates
|
||||
// (this is called a "memory leak"):
|
||||
free(my_ptr);
|
||||
|
||||
|
||||
// Strings are arrays of char, but they are usually represented as a
|
||||
// pointer-to-char (which is a pointer to the first element of the array).
|
||||
// It's good practice to use `const char *' when referring to a string literal,
|
||||
// since string literals shall not be modified (i. e. "foo"[0] = 'a' is ILLEGAL.)
|
||||
const char *my_str = "This is my very own string literal";
|
||||
printf("%c\n", *my_str); // => 'T'
|
||||
|
||||
// This is not the case if the string is an array (potentially initialized with a string literal)
|
||||
|
||||
// This is not the case if the string is an array
|
||||
// (potentially initialized with a string literal)
|
||||
// that resides in writable memory, as in:
|
||||
char foo[] = "foo";
|
||||
foo[0] = 'a'; // this is legal, foo now contains "aoo"
|
||||
|
||||
|
||||
function_1();
|
||||
} // end main function
|
||||
|
||||
@ -435,17 +416,17 @@ printf("%s\n", c); // => ".tset a si sihT"
|
||||
typedef int my_type;
|
||||
my_type my_type_var = 0;
|
||||
|
||||
// Structs are just collections of data, the members are allocated sequentially, in the order they are written:
|
||||
// Structs are just collections of data, the members are allocated sequentially,
|
||||
// in the order they are written:
|
||||
struct rectangle {
|
||||
int width;
|
||||
int height;
|
||||
};
|
||||
|
||||
// it's generally not true that sizeof(struct rectangle) == sizeof(int) + sizeof(int) due to
|
||||
// potential padding between the structure members (this is for alignment reasons. Probably won't
|
||||
// happen if all members are of the same type, but watch out!
|
||||
// See http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member
|
||||
// for further information.
|
||||
// It's not generally true that
|
||||
// sizeof(struct rectangle) == sizeof(int) + sizeof(int)
|
||||
// due to potential padding between the structure members (this is for alignment
|
||||
// reasons). [1]
|
||||
|
||||
void function_1()
|
||||
{
|
||||
@ -473,7 +454,8 @@ int area(rect r)
|
||||
return r.width * r.height;
|
||||
}
|
||||
|
||||
// if you have large structs, you can pass them "by pointer" to avoid copying the whole struct:
|
||||
// if you have large structs, you can pass them "by pointer" to avoid copying
|
||||
// the whole struct:
|
||||
int area(const rect *r)
|
||||
{
|
||||
return r->width * r->height;
|
||||
@ -527,3 +509,5 @@ Readable code is better than clever code and fast code. For a good, sane coding
|
||||
[Linux kernel coding stlye](https://www.kernel.org/doc/Documentation/CodingStyle).
|
||||
|
||||
Other than that, Google is your friend.
|
||||
|
||||
[1] http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member
|
||||
|
||||
@ -1,5 +1,6 @@
|
||||
---
|
||||
language: java
|
||||
filename: java-kr.java
|
||||
category: language
|
||||
contributors:
|
||||
- ["Jake Prather", "http://github.com/JakeHP"]
|
||||
@ -26,7 +27,8 @@ import java.util.ArrayList;
|
||||
// java.security 패키지 안에 있는 모든 클래스를 임포트합니다.
|
||||
import java.security.*;
|
||||
|
||||
// 각 .java 파일에는 공용(public) 클래스가 들어 있으며, 클래스의 이름은 파일명과 동일합니다.
|
||||
// 각 .java 파일에는 공용(public) 클래스가 들어 있으며, 클래스의 이름은
|
||||
// 파일명과 동일합니다.
|
||||
public class LearnJava {
|
||||
|
||||
// 프로그램에는 반드시 진입점 역할을 하는 main 메서드가 하나 있어야 합니다.
|
||||
@ -253,8 +255,8 @@ public class LearnJava {
|
||||
// String
|
||||
|
||||
// 형변환
|
||||
// 자바 객채 또한 형변환할 수 있으며, 이와 관련해서 알아야 할 세부사항이 많을뿐더러
|
||||
// 다소 중급 수준에 해당하는 개념들도 다뤄야 합니다.
|
||||
// 자바 객채 또한 형변환할 수 있으며, 이와 관련해서 알아야 할 세부사항이
|
||||
// 많을뿐더러 다소 중급 수준에 해당하는 개념들도 다뤄야 합니다.
|
||||
// 이와 관련된 사항은 아래 링크를 참고하세요.
|
||||
// http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
|
||||
|
||||
@ -403,4 +405,4 @@ class PennyFarthing extends Bicycle {
|
||||
|
||||
* [제네릭(Generics)](http://docs.oracle.com/javase/tutorial/java/generics/index.html)
|
||||
|
||||
* [자바 코딩 관례(Java Code Conventions)](http://www.oracle.com/technetwork/java/codeconv-138413.html)
|
||||
* [자바 코딩 관례(Java Code Conventions)](http://www.oracle.com/technetwork/java/codeconv-138413.html)
|
||||
|
||||
@ -1,5 +1,6 @@
|
||||
---
|
||||
language: ruby
|
||||
lang: br-pt
|
||||
filename: learnruby.rb
|
||||
contributors:
|
||||
- ["Bruno Henrique - Garu", "http://garulab.com"]
|
||||
@ -98,9 +99,10 @@ caminho_para_a_raiz_do_projeto = '/bom/nome/'
|
||||
caminho = '/nome/ruim/'
|
||||
|
||||
# Símbolos (são objetos)
|
||||
# Símbolos são imutáveis, são constantes reutilizáveis representadadas internamente por um
|
||||
# valor inteiro. Eles são frequentemente usados no lugar de strings para transmitir com eficiência os valores
|
||||
# específicos e significativos
|
||||
# Símbolos são imutáveis, são constantes reutilizáveis representadadas
|
||||
# internamente por um valor inteiro. Eles são frequentemente usados no
|
||||
# lugar de strings para transmitir com eficiência os valores específicos
|
||||
# e significativos
|
||||
|
||||
:pendente.class #=> Symbol
|
||||
|
||||
|
||||
@ -4,7 +4,7 @@ filename: learnclojure-ru.clj
|
||||
contributors:
|
||||
- ["Adam Bard", "http://adambard.com/"]
|
||||
- ["Alexey Pirogov", "http://twitter.com/alex_pir"]
|
||||
|
||||
lang: ru-ru
|
||||
---
|
||||
|
||||
Clojure, это представитель семейства Lisp-подобных языков, разработанный
|
||||
|
||||
@ -88,7 +88,8 @@ $unescaped = 'This just contains a slash and a t: \t';
|
||||
// Заключайте переменные в фигурные скобки если это необходимо
|
||||
$money = "I have $${number} in the bank.";
|
||||
|
||||
// Начиная с PHP 5.3, синтаксис nowdocs может использоваться для неинтерполированного многострочного текста
|
||||
// Начиная с PHP 5.3, синтаксис nowdocs может использоваться для
|
||||
// неинтерполированного многострочного текста
|
||||
$nowdoc = <<<'END'
|
||||
Multi line
|
||||
string
|
||||
@ -210,11 +211,13 @@ echo $integer + $integer; // => 2
|
||||
$string = '1';
|
||||
echo $string + $string; // => 2 (строка превращается в число)
|
||||
|
||||
// Выводится 0 по той причине, что оператор + не может привести строку 'one' к числовому типу
|
||||
// Выводится 0 по той причине, что оператор + не может привести строку 'one' к
|
||||
// числовому типу
|
||||
$string = 'one';
|
||||
echo $string + $string; // => 0
|
||||
|
||||
// Приведение типов (type casting) может быть использовано для преобразование переменной в другой тип
|
||||
// Приведение типов (type casting) может быть использовано для преобразование
|
||||
// переменной в другой тип
|
||||
$boolean = (boolean) 1; // => true
|
||||
|
||||
$zero = 0;
|
||||
@ -429,10 +432,11 @@ return 'Anything you like.';
|
||||
// Эти функции могут также возвращать значения.
|
||||
$value = include 'my-include.php';
|
||||
|
||||
// Имена файлов содержат их путь в файловой системе, или если передано просто имя файла,
|
||||
// PHP обращается к директиве include_path. Если файл не найден в include_path, предпринимается
|
||||
// попытка поиска в папке, где выполняется скрипт или в текущей рабочей директории.
|
||||
// Если не в одном из этих мест файл не найден - выдается ошибка
|
||||
// Имена файлов содержат их путь в файловой системе, или если передано просто
|
||||
// имя файла, PHP обращается к директиве include_path. Если файл не найден в
|
||||
// include_path, предпринимается попытка поиска в папке, где выполняется скрипт
|
||||
// или в текущей рабочей директории. Если не в одном из этих мест файл не
|
||||
// найден - выдается ошибка
|
||||
/* */
|
||||
|
||||
/********************************
|
||||
|
||||
@ -1,5 +1,6 @@
|
||||
---
|
||||
language: python
|
||||
lang: ru-ru
|
||||
contributors:
|
||||
- ["Yury Timofeev", "http://twitter.com/gagar1n"]
|
||||
filename: learnpython-ru.py
|
||||
@ -219,7 +220,8 @@ filled_dict["four"] # KeyError
|
||||
# Чтобы избежать этого, используйте метод get
|
||||
filled_dict.get("one") #=> 1
|
||||
filled_dict.get("four") #=> None
|
||||
# Метод get также принимает аргумент default, значение которого будет возвращено при отсутствии указанного ключа
|
||||
# Метод get также принимает аргумент default, значение которого будет
|
||||
# возвращено при отсутствии указанного ключа
|
||||
filled_dict.get("one", 4) #=> 1
|
||||
filled_dict.get("four", 4) #=> 4
|
||||
|
||||
@ -314,7 +316,9 @@ try:
|
||||
# Для выбора ошибки используется raise
|
||||
raise IndexError("Это IndexError")
|
||||
except IndexError as e:
|
||||
pass # pass это просто отсутствие оператора. Обычно здесь происходит восстановление от ошибки.
|
||||
# pass это просто отсутствие оператора. Обычно здесь происходит
|
||||
# восстановление от ошибки.
|
||||
pass
|
||||
|
||||
|
||||
####################################################
|
||||
|
||||
@ -29,7 +29,8 @@ import (
|
||||
"strconv" // 字符串转换
|
||||
)
|
||||
|
||||
//函数声明：Main是程序执行的入口。不管你喜欢还是不喜欢，反正G就用了花括号来包住函数体。
|
||||
// 函数声明：Main是程序执行的入口。
|
||||
// 不管你喜欢还是不喜欢，反正G就用了花括号来包住函数体。
|
||||
func main() {
|
||||
// 往标准输出打印一行。
|
||||
// 用包名fmt限制打印函数。
|
||||
@ -65,10 +66,10 @@ func learnTypes() {
|
||||
can include line breaks.` // 同样是String类型
|
||||
|
||||
// 非ascii字符。Go使用UTF-8编码。
|
||||
g := 'Σ' // rune类型，uint32的别名，使用UTF-8编码
|
||||
g := 'Σ' // rune类型，uint32的别名，使用UTF-8编码
|
||||
|
||||
f := 3.14195 // float64类型，IEEE-754 64位浮点数
|
||||
c := 3 + 4i // complex128类型，内部使用两个float64表示
|
||||
f := 3.14195 // float64类型，IEEE-754 64位浮点数
|
||||
c := 3 + 4i // complex128类型，内部使用两个float64表示
|
||||
|
||||
// Var变量可以直接初始化。
|
||||
var u uint = 7 // unsigned 无符号变量，但是实现依赖int型变量的长度
|
||||
@ -99,9 +100,9 @@ can include line breaks.` // 同样是String类型
|
||||
// 下划线 _ 可以使你“使用”一个变量，但是丢弃它的值。
|
||||
_,_,_,_,_,_,_,_,_ = s2, g, f, u, pi, n, a3, s4, bs
|
||||
// 输出变量
|
||||
fmt.Println(s, c, a4, s3, d2, m)
|
||||
fmt.Println(s, c, a4, s3, d2, m)
|
||||
|
||||
learnFlowControl() // 回到流程控制
|
||||
learnFlowControl() // 回到流程控制
|
||||
}
|
||||
|
||||
// Go全面支持垃圾回收。Go有指针，但是不支持指针运算。
|
||||
@ -117,155 +118,159 @@ func learnMemory() (p, q *int) {
|
||||
}
|
||||
|
||||
func expensiveComputation() int {
|
||||
return 1e6
|
||||
return 1e6
|
||||
}
|
||||
|
||||
func learnFlowControl() {
|
||||
// If需要花括号，括号就免了
|
||||
if true {
|
||||
fmt.Println("told ya")
|
||||
}
|
||||
// 用go fmt 命令可以帮你格式化代码，所以不用怕被人吐槽代码风格了，也不用容忍被人的代码风格。
|
||||
if false {
|
||||
// pout
|
||||
} else {
|
||||
// gloat
|
||||
}
|
||||
if true {
|
||||
fmt.Println("told ya")
|
||||
}
|
||||
// 用go fmt 命令可以帮你格式化代码，所以不用怕被人吐槽代码风格了，
|
||||
// 也不用容忍被人的代码风格。
|
||||
if false {
|
||||
// pout
|
||||
} else {
|
||||
// gloat
|
||||
}
|
||||
// 如果太多嵌套的if语句，推荐使用switch
|
||||
x := 1
|
||||
switch x {
|
||||
case 0:
|
||||
case 1:
|
||||
x := 1
|
||||
switch x {
|
||||
case 0:
|
||||
case 1:
|
||||
// 隐式调用break语句，匹配上一个即停止
|
||||
case 2:
|
||||
case 2:
|
||||
// 不会运行
|
||||
}
|
||||
}
|
||||
// 和if一样，for也不用括号
|
||||
for x := 0; x < 3; x++ { // ++ 自增
|
||||
fmt.Println("iteration", x)
|
||||
}
|
||||
for x := 0; x < 3; x++ { // ++ 自增
|
||||
fmt.Println("iteration", x)
|
||||
}
|
||||
// x在这里还是1。为什么？
|
||||
|
||||
// for 是go里唯一的循环关键字，不过它有很多变种
|
||||
for { // 无限循环
|
||||
break // 骗你的
|
||||
continue // 不会运行的
|
||||
}
|
||||
for { // 无限循环
|
||||
break // 骗你的
|
||||
continue // 不会运行的
|
||||
}
|
||||
// 和for一样，if中的:=先给y赋值，然后再和x作比较。
|
||||
if y := expensiveComputation(); y > x {
|
||||
x = y
|
||||
}
|
||||
if y := expensiveComputation(); y > x {
|
||||
x = y
|
||||
}
|
||||
// 闭包函数
|
||||
xBig := func() bool {
|
||||
return x > 100 // x是上面声明的变量引用
|
||||
}
|
||||
fmt.Println("xBig:", xBig()) // true （上面把y赋给x了）
|
||||
x /= 1e5 // x变成10
|
||||
fmt.Println("xBig:", xBig()) // 现在是false
|
||||
xBig := func() bool {
|
||||
return x > 100 // x是上面声明的变量引用
|
||||
}
|
||||
fmt.Println("xBig:", xBig()) // true （上面把y赋给x了）
|
||||
x /= 1e5 // x变成10
|
||||
fmt.Println("xBig:", xBig()) // 现在是false
|
||||
|
||||
// 当你需要goto的时候，你会爱死它的！
|
||||
goto love
|
||||
goto love
|
||||
love:
|
||||
|
||||
learnInterfaces() // 好东西来了！
|
||||
learnInterfaces() // 好东西来了！
|
||||
}
|
||||
|
||||
// 定义Stringer为一个接口类型，有一个方法String
|
||||
type Stringer interface {
|
||||
String() string
|
||||
String() string
|
||||
}
|
||||
|
||||
// 定义pair为一个结构体，有x和y两个int型变量。
|
||||
type pair struct {
|
||||
x, y int
|
||||
x, y int
|
||||
}
|
||||
|
||||
// 定义pair类型的方法，实现Stringer接口。
|
||||
func (p pair) String() string { // p被叫做“接收器”
|
||||
// Sprintf是fmt包中的另一个公有函数。
|
||||
// 用 . 调用p中的元素。
|
||||
return fmt.Sprintf("(%d, %d)", p.x, p.y)
|
||||
return fmt.Sprintf("(%d, %d)", p.x, p.y)
|
||||
}
|
||||
|
||||
func learnInterfaces() {
|
||||
// 花括号用来定义结构体变量，:=在这里将一个结构体变量赋值给p。
|
||||
p := pair{3, 4}
|
||||
fmt.Println(p.String()) // 调用pair类型p的String方法
|
||||
var i Stringer // 声明i为Stringer接口类型
|
||||
i = p // 有效！因为p实现了Stringer接口（类似java中的塑型）
|
||||
p := pair{3, 4}
|
||||
fmt.Println(p.String()) // 调用pair类型p的String方法
|
||||
var i Stringer // 声明i为Stringer接口类型
|
||||
i = p // 有效！因为p实现了Stringer接口（类似java中的塑型）
|
||||
// 调用i的String方法，输出和上面一样
|
||||
fmt.Println(i.String())
|
||||
fmt.Println(i.String())
|
||||
|
||||
// fmt包中的Println函数向对象要它们的string输出，实现了String方法就可以这样使用了。（类似java中的序列化）
|
||||
fmt.Println(p) // 输出和上面一样，自动调用String函数。
|
||||
fmt.Println(i) // 输出和上面一样。
|
||||
// fmt包中的Println函数向对象要它们的string输出，实现了String方法就可以这样使用了。
|
||||
// （类似java中的序列化）
|
||||
fmt.Println(p) // 输出和上面一样，自动调用String函数。
|
||||
fmt.Println(i) // 输出和上面一样。
|
||||
|
||||
learnErrorHandling()
|
||||
learnErrorHandling()
|
||||
}
|
||||
|
||||
func learnErrorHandling() {
|
||||
// ", ok"用来判断有没有正常工作
|
||||
m := map[int]string{3: "three", 4: "four"}
|
||||
if x, ok := m[1]; !ok { // ok 为false，因为m中没有1
|
||||
fmt.Println("no one there")
|
||||
} else {
|
||||
fmt.Print(x) // 如果x在map中的话，x就是那个值喽。
|
||||
}
|
||||
// ", ok"用来判断有没有正常工作
|
||||
m := map[int]string{3: "three", 4: "four"}
|
||||
if x, ok := m[1]; !ok { // ok 为false，因为m中没有1
|
||||
fmt.Println("no one there")
|
||||
} else {
|
||||
fmt.Print(x) // 如果x在map中的话，x就是那个值喽。
|
||||
}
|
||||
// 错误可不只是ok，它还可以给出关于问题的更多细节。
|
||||
if _, err := strconv.Atoi("non-int"); err != nil { // _ discards value
|
||||
// 输出"strconv.ParseInt: parsing "non-int": invalid syntax"
|
||||
fmt.Println(err)
|
||||
}
|
||||
if _, err := strconv.Atoi("non-int"); err != nil { // _ discards value
|
||||
// 输出"strconv.ParseInt: parsing "non-int": invalid syntax"
|
||||
fmt.Println(err)
|
||||
}
|
||||
// 待会再说接口吧。同时，
|
||||
learnConcurrency()
|
||||
learnConcurrency()
|
||||
}
|
||||
|
||||
// c是channel类型，一个并发安全的通信对象。
|
||||
func inc(i int, c chan int) {
|
||||
c <- i + 1 // <-把右边的发送到左边的channel。
|
||||
c <- i + 1 // <-把右边的发送到左边的channel。
|
||||
}
|
||||
|
||||
// 我们将用inc函数来并发地增加一些数字。
|
||||
func learnConcurrency() {
|
||||
// 用make来声明一个slice，make会分配和初始化slice，map和channel。
|
||||
c := make(chan int)
|
||||
// 用go关键字开始三个并发的goroutine，如果机器支持的话，还可能是并行执行。三个都被发送到同一个channel。
|
||||
go inc(0, c) // go is a statement that starts a new goroutine.
|
||||
go inc(10, c)
|
||||
go inc(-805, c)
|
||||
c := make(chan int)
|
||||
// 用go关键字开始三个并发的goroutine，如果机器支持的话，还可能是并行执行。
|
||||
// 三个都被发送到同一个channel。
|
||||
go inc(0, c) // go is a statement that starts a new goroutine.
|
||||
go inc(10, c)
|
||||
go inc(-805, c)
|
||||
// 从channel中独处结果并打印。
|
||||
// 打印出什么东西是不可预知的。
|
||||
fmt.Println(<-c, <-c, <-c) // channel在右边的时候，<-是接收操作。
|
||||
fmt.Println(<-c, <-c, <-c) // channel在右边的时候，<-是接收操作。
|
||||
|
||||
cs := make(chan string) // 操作string的channel
|
||||
cc := make(chan chan string) // 操作channel的channel
|
||||
go func() { c <- 84 }() // 开始一个goroutine来发送一个新的数字
|
||||
go func() { cs <- "wordy" }() // 发送给cs
|
||||
// Select类似于switch，但是每个case包括一个channel操作。它随机选择一个准备好通讯的case。
|
||||
select {
|
||||
case i := <-c: // 从channel接收的值可以赋给其他变量
|
||||
fmt.Println("it's a", i)
|
||||
case <-cs: // 或者直接丢弃
|
||||
fmt.Println("it's a string")
|
||||
case <-cc: // 空的，还没作好通讯的准备
|
||||
fmt.Println("didn't happen.")
|
||||
}
|
||||
cs := make(chan string) // 操作string的channel
|
||||
cc := make(chan chan string) // 操作channel的channel
|
||||
go func() { c <- 84 }() // 开始一个goroutine来发送一个新的数字
|
||||
go func() { cs <- "wordy" }() // 发送给cs
|
||||
// Select类似于switch，但是每个case包括一个channel操作。
|
||||
// 它随机选择一个准备好通讯的case。
|
||||
select {
|
||||
case i := <-c: // 从channel接收的值可以赋给其他变量
|
||||
fmt.Println("it's a", i)
|
||||
case <-cs: // 或者直接丢弃
|
||||
fmt.Println("it's a string")
|
||||
case <-cc: // 空的，还没作好通讯的准备
|
||||
fmt.Println("didn't happen.")
|
||||
}
|
||||
// 上面c或者cs的值被取到，其中一个goroutine结束，另外一个保持阻塞。
|
||||
|
||||
learnWebProgramming() // Go很适合web编程，我知道你也想学！
|
||||
learnWebProgramming() // Go很适合web编程，我知道你也想学！
|
||||
}
|
||||
|
||||
// http包中的一个简单的函数就可以开启web服务器。
|
||||
func learnWebProgramming() {
|
||||
// ListenAndServe第一个参数指定了监听端口，第二个参数是一个接口，特定是http.Handler。
|
||||
err := http.ListenAndServe(":8080", pair{})
|
||||
fmt.Println(err) // 不要无视错误。
|
||||
err := http.ListenAndServe(":8080", pair{})
|
||||
fmt.Println(err) // 不要无视错误。
|
||||
}
|
||||
|
||||
// 使pair实现http.Handler接口的ServeHTTP方法。
|
||||
func (p pair) ServeHTTP(w http.ResponseWriter, r *http.Request) {
|
||||
// 使用http.ResponseWriter返回数据
|
||||
w.Write([]byte("You learned Go in Y minutes!"))
|
||||
w.Write([]byte("You learned Go in Y minutes!"))
|
||||
}
|
||||
```
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user