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diff --git a/c.html.markdown b/c.html.markdown index 2b50efa0..8e16837c 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -1,23 +1,25 @@ --- -name: c -category: language -language: c -filename: learnc.c -contributors: - - ["Adam Bard", "http://adambard.com/"] +- name: c +- category: language +- language: c +- filename: learnc.c +- contributors: + - [Adam Bard](http://adambard.com/) + - [Árpád Goretity](http://twitter.com/H2CO3_iOS) + --- -Ah, C. Still the language of modern high-performance computing. +Ah, C. Still **the** language of modern high-performance computing. C is the lowest-level language most programmers will ever use, but it more than makes up for it with raw speed. Just be aware of its manual memory management and C will take you as far as you need to go. ```c -// Single-line comments start with // +// Single-line comments start with // - only available in C99 and later. /* -Multi-line comments look like this. +Multi-line comments look like this. They work in C89 as well. */ // Import headers with #include @@ -25,6 +27,17 @@ Multi-line comments look like this. #include <stdio.h> #include <string.h> +// file names between <angle brackets> are headers from the C standard library. +// They are searched for by the preprocessor in the system include paths +// (usually /usr/lib on Unices, can be controlled with the -I<dir> option if you are using GCC or clang.) +// For your own headers, use double quotes instead of angle brackets: +#include "my_header.h" + +// The C preprocessor introduces an almost fully-featured macro language. It's useful, but +// it can be confusing (and what's even worse, it can be misused). Read the +// Wikipedia article on the C preprocessor for further information: +// http://en.wikipedia.org/wiki/C_preprocessor + // Declare function signatures in advance in a .h file, or at the top of // your .c file. void function_1(); @@ -33,264 +46,347 @@ void function_2(); // Your program's entry point is a function called // main with an integer return type. int main() { - -// print output using printf, for "print formatted" -// %d is an integer, \n is a newline -printf("%d\n", 0); // => Prints 0 -// All statements must end with a semicolon - -/////////////////////////////////////// -// Types -/////////////////////////////////////// - -// You have to declare variables before using them. A variable declaration -// requires you to specify its type; a variable's type determines its size -// in bytes. - -// ints are usually 4 bytes -int x_int = 0; - -// shorts are usually 2 bytes -short x_short = 0; - -// chars are guaranteed to be 1 byte -char x_char = 0; -char y_char = 'y'; // Char literals are quoted with '' - -// longs are often 4 to 8 bytes; long longs are guaranteed to be at least -// 64 bits -long x_long = 0; -long long x_long_long = 0; - -// floats are usually 32-bit floating point numbers -float x_float = 0.0; - -// doubles are usually 64-bit floating-point numbers -double x_double = 0.0; - -// Integral types may be unsigned. This means they can't be negative, but -// the maximum value of an unsigned variable is greater than the maximum -// signed value of the same size. -unsigned char ux_char; -unsigned short ux_short; -unsigned int ux_int; -unsigned long long ux_long_long; - -// Other than char, which is always 1 byte, these types vary in size depending -// on your machine. sizeof(T) gives you the size of a variable with type T in -// bytes so you can express the size of these types in a portable way. -// For example, -printf("%lu\n", sizeof(int)); // => 4 (on machines with 4-byte words) - -// Arrays must be initialized with a concrete size. -char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes -int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes - // (assuming 4-byte words) - - -// You can initialize an array to 0 thusly: -char my_array[20] = {0}; - -// Indexing an array is like other languages -- or, -// rather, other languages are like C -my_array[0]; // => 0 - -// Arrays are mutable; it's just memory! -my_array[1] = 2; -printf("%d\n", my_array[1]); // => 2 - -// Strings are just arrays of chars terminated by a NUL (0x00) byte, -// represented in strings as the special character '\0'. -// (We don't have to include the NUL byte in string literals; the compiler -// inserts it at the end of the array for us.) -char a_string[20] = "This is a string"; -printf("%s\n", a_string); // %s formats a string - -/* -You may have noticed that a_string is only 16 chars long. -Char #17 is the NUL byte. -Chars #18, 19 and 20 have undefined values. -*/ - -printf("%d\n", a_string[16]); // => 0 - -/////////////////////////////////////// -// Operators -/////////////////////////////////////// - -int i1 = 1, i2 = 2; // Shorthand for multiple declaration -float f1 = 1.0, f2 = 2.0; - -// Arithmetic is straightforward -i1 + i2; // => 3 -i2 - i1; // => 1 -i2 * i1; // => 2 -i1 / i2; // => 0 (0.5, but truncated towards 0) - -f1 / f2; // => 0.5, plus or minus epsilon - -// Modulo is there as well -11 % 3; // => 2 - -// Comparison operators are probably familiar, but -// there is no boolean type in c. We use ints instead. -// 0 is false, anything else is true. (The comparison -// operators always return 0 or 1.) -3 == 2; // => 0 (false) -3 != 2; // => 1 (true) -3 > 2; // => 1 -3 < 2; // => 0 -2 <= 2; // => 1 -2 >= 2; // => 1 - -// Logic works on ints -!3; // => 0 (Logical not) -!0; // => 1 -1 && 1; // => 1 (Logical and) -0 && 1; // => 0 -0 || 1; // => 1 (Logical or) -0 || 0; // => 0 - -// Bitwise operators! -~0x0F; // => 0xF0 (bitwise negation) -0x0F & 0xF0; // => 0x00 (bitwise AND) -0x0F | 0xF0; // => 0xFF (bitwise OR) -0x04 ^ 0x0F; // => 0x0B (bitwise XOR) -0x01 << 1; // => 0x02 (bitwise left shift (by 1)) -0x02 >> 1; // => 0x01 (bitwise right shift (by 1)) - -/////////////////////////////////////// -// Control Structures -/////////////////////////////////////// - -if (0) { - printf("I am never run\n"); -} else if (0) { - printf("I am also never run\n"); -} else { - printf("I print\n"); -} - -// While loops exist -int ii = 0; -while (ii < 10) { - printf("%d, ", ii++); // ii++ increments ii in-place, after using its value. -} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " - -printf("\n"); - -int kk = 0; -do { - printf("%d, ", kk); -} while (++kk < 10); // ++kk increments kk in-place, before using its value -// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " - -printf("\n"); - -// For loops too -int jj; -for (jj=0; jj < 10; jj++) { - printf("%d, ", jj); -} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " - -printf("\n"); - -/////////////////////////////////////// -// Typecasting -/////////////////////////////////////// - -// Every value in C has a type, but you can cast one value into another type -// if you want. - -int x_hex = 0x01; // You can assign vars with hex literals - -// Casting between types will attempt to preserve their numeric values -printf("%d\n", x_hex); // => Prints 1 -printf("%d\n", (short) x_hex); // => Prints 1 -printf("%d\n", (char) x_hex); // => Prints 1 - -// Types will overflow without warning -printf("%d\n", (char) 257); // => 1 (Max char = 255) - -// Integral types can be cast to floating-point types, and vice-versa. -printf("%f\n", (float)100); // %f formats a float -printf("%lf\n", (double)100); // %lf formats a double -printf("%d\n", (char)100.0); - -/////////////////////////////////////// -// Pointers -/////////////////////////////////////// - -// A pointer is a variable declared to store a memory address. Its declaration will -// also tell you the type of data it points to. You can retrieve the memory address -// of your variables, then mess with them. - -int x = 0; -printf("%p\n", &x); // Use & to retrieve the address of a variable -// (%p formats a pointer) -// => Prints some address in memory; - - -// Pointers start with * in their declaration -int *px, not_a_pointer; // px is a pointer to an int -px = &x; // Stores the address of x in px -printf("%p\n", px); // => Prints some address in memory -printf("%d, %d\n", (int)sizeof(px), (int)sizeof(not_a_pointer)); -// => Prints "8, 4" on 64-bit system - -// To retreive the value at the address a pointer is pointing to, -// put * in front to de-reference it. -printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of - -// 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 -printf("%d\n", *px); // => Prints 1 -printf("%d\n", x); // => Prints 1 - -int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory -int xx; -for (xx=0; xx<20; xx++) { - 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). -// This works because arrays are actually just pointers to their first element. - -// Arrays are pointers to their first element -printf("%d\n", *(x_ptr)); // => Prints 20 -printf("%d\n", x_array[0]); // => Prints 20 - -// Pointers are incremented and decremented based on their type -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 integer argument -// representing the number of bytes to allocate from the heap. -int* my_ptr = (int*) malloc(sizeof(int) * 20); -for (xx=0; xx<20; xx++) { - *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here -} // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints) - -// Dereferencing memory that you haven't allocated gives -// unpredictable results -printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? - -// 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 -free(my_ptr); - -// Strings can be char arrays, but are usually represented as char -// pointers: -char* my_str = "This is my very own string"; - -printf("%c\n", *my_str); // => 'T' - -function_1(); + // print output using printf, for "print formatted" + // %d is an integer, \n is a newline + printf("%d\n", 0); // => Prints 0 + // All statements must end with a semicolon + + /////////////////////////////////////// + // Types + /////////////////////////////////////// + + // You have to declare variables before using them. A variable declaration + // requires you to specify its type; a variable's type determines its size + // in bytes. + + // ints are usually 4 bytes + int x_int = 0; + + // shorts are usually 2 bytes + short x_short = 0; + + // chars are guaranteed to be 1 byte + char x_char = 0; + char y_char = 'y'; // Char literals are quoted with '' + + // longs are often 4 to 8 bytes; long longs are guaranteed to be at least + // 64 bits + long x_long = 0; + long long x_long_long = 0; + + // floats are usually 32-bit floating point numbers + float x_float = 0.0; + + // doubles are usually 64-bit floating-point numbers + double x_double = 0.0; + + // Integral types may be unsigned. This means they can't be negative, but + // the maximum value of an unsigned variable is greater than the maximum + // signed value of the same size. + unsigned char ux_char; + unsigned short ux_short; + unsigned int ux_int; + unsigned long long ux_long_long; + + // Other than char, which is always 1 byte (but not necessarily 8 bits!), + // these types vary in size depending on your machine and compiler. + // sizeof(T) gives you the size of a variable with type T in + // bytes so you can express the size of these types in a portable way. + // sizeof(obj) yields the size of an actual expression (variable, literal, etc.). + // For example, + printf("%zu\n", sizeof(int)); // => 4 (on most machines with 4-byte words) + + + // It's worth noting that if the argument of the `sizeof` operator is not a type but an expression, + // then its argument is not evaluated except VLAs (see below). Also, `sizeof()` is an operator, not a function, + // furthermore, the value it yields is a compile-time constant (except when used on VLAs, again.) + int a = 1; + size_t size = sizeof(a++); // a++ is not evaluated + printf("sizeof(a++) = %zu where a = %d\n", size, a); + // the above code prints "sizeof(a++) = 4 where a = 1" (on a usual 32-bit architecture) + + // Arrays must be initialized with a concrete size. + char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes + int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes + // (assuming 4-byte words) + + + // You can initialize an array to 0 thusly: + char my_array[20] = {0}; + + // Indexing an array is like other languages -- or, + // rather, other languages are like C + my_array[0]; // => 0 + + // Arrays are mutable; it's just memory! + my_array[1] = 2; + printf("%d\n", my_array[1]); // => 2 + + // In C99 (and as an optional feature in C11), variable-length arrays (VLAs) can be declared as well. + // The size of such an array need not be a compile time constant: + printf("Enter the array size: "); // ask the user for an array size + char buf[0x100]; + fgets(buf, sizeof buf, stdin); + size_t size = strtoul(buf, NULL, 10); // strtoul parses a string to an unsigned integer + int var_length_array[size]; // declare the VLA + printf("sizeof array = %zu\n", sizeof var_length_array); + + // A possible outcome of this program may be: + Enter the array size: 10 + sizeof array = 40 + + // Strings are just arrays of chars terminated by a NUL (0x00) byte, + // represented in strings as the special character '\0'. + // (We don't have to include the NUL byte in string literals; the compiler + // inserts it at the end of the array for us.) + char a_string[20] = "This is a string"; + printf("%s\n", a_string); // %s formats a string + + /* + You may have noticed that a_string is only 16 chars long. + Char #17 is the NUL byte. + Chars #18, 19 and 20 are 0 as well - if an initializer list (in this case, the string literal) + has less elements than the array it is initializing, then excess array elements are implicitly + initialized to zero. This is why int ar[10] = { 0 } works as expected intuitively. + */ + + printf("%d\n", a_string[16]); // => 0 + + // So string literals are strings enclosed within double quotes, but if we have characters + // between single quotes, that's a character literal. + // It's of type `int`, and *not* `char` (for historical reasons). + int cha = 'a'; // fine + char chb = 'a'; // fine too (implicit conversion from int to char - truncation) + + /////////////////////////////////////// + // Operators + /////////////////////////////////////// + + int i1 = 1, i2 = 2; // Shorthand for multiple declaration + float f1 = 1.0, f2 = 2.0; + + // Arithmetic is straightforward + i1 + i2; // => 3 + i2 - i1; // => 1 + i2 * i1; // => 2 + i1 / i2; // => 0 (0.5, but truncated towards 0) + + f1 / f2; // => 0.5, plus or minus epsilon - floating-point numbers and calculations are not exact + + // Modulo is there as well + 11 % 3; // => 2 + + // Comparison operators are probably familiar, but + // there is no boolean type in c. We use ints instead. + // (Or _Bool or bool in C99.) + // 0 is false, anything else is true. (The comparison + // operators always yield 0 or 1.) + 3 == 2; // => 0 (false) + 3 != 2; // => 1 (true) + 3 > 2; // => 1 + 3 < 2; // => 0 + 2 <= 2; // => 1 + 2 >= 2; // => 1 + + // C is not Python - comparisons don't chain. + int a = 1; + // WRONG: + int between_0_and_2 = 0 < a < 2; + // Correct: + int between_0_and_2 = 0 < a && a < 2; + + // Logic works on ints + !3; // => 0 (Logical not) + !0; // => 1 + 1 && 1; // => 1 (Logical and) + 0 && 1; // => 0 + 0 || 1; // => 1 (Logical or) + 0 || 0; // => 0 + + // Bitwise operators! + ~0x0F; // => 0xF0 (bitwise negation, "1's complement") + 0x0F & 0xF0; // => 0x00 (bitwise AND) + 0x0F | 0xF0; // => 0xFF (bitwise OR) + 0x04 ^ 0x0F; // => 0x0B (bitwise XOR) + 0x01 << 1; // => 0x02 (bitwise left shift (by 1)) + 0x02 >> 1; // => 0x01 (bitwise right shift (by 1)) + + // Be careful when shifting signed integers - the following are all undefined behavior: + // - shifting into the sign bit of a signed integer (int a = 1 << 32) + // - left-shifting a negative number (int a = -1 << 2) + // - shifting by an offset which is more than or equal to the width of the type of the LHS: + // int a = 1 << 32; // UB if int is 32 bits wide + + /////////////////////////////////////// + // Control Structures + /////////////////////////////////////// + + if (0) { + printf("I am never run\n"); + } else if (0) { + printf("I am also never run\n"); + } else { + printf("I print\n"); + } + + // While loops exist + int ii = 0; + while (ii < 10) { + printf("%d, ", ii++); // ii++ increments ii in-place, after yielding its value ("postincrement"). + } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); + + int kk = 0; + do { + printf("%d, ", kk); + } while (++kk < 10); // ++kk increments kk in-place, and yields the already incremented value ("preincrement") + // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); + + // For loops too + int jj; + for (jj=0; jj < 10; jj++) { + printf("%d, ", jj); + } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); + + // branching with multiple choices: switch() + switch (some_integral_expression) { + case 0: // labels need to be integral *constant* epxressions + do_stuff(); + break; // if you don't break, control flow falls over labels - you usually don't want that. + case 1: + do_something_else(); + break; + default: + // if `some_integral_expression` didn't match any of the labels + fputs("error!\n", stderr); + exit(-1); + break; + } + + + /////////////////////////////////////// + // Typecasting + /////////////////////////////////////// + + // Every value in C has a type, but you can cast one value into another type + // if you want (with some constraints). + + int x_hex = 0x01; // You can assign vars with hex literals + + // Casting between types will attempt to preserve their numeric values + printf("%d\n", x_hex); // => Prints 1 + printf("%d\n", (short) x_hex); // => Prints 1 + printf("%d\n", (char) x_hex); // => Prints 1 + + // Types will overflow without warning + printf("%d\n", (unsigned char) 257); // => 1 (Max char = 255 if char is 8 bits long) + // printf("%d\n", (unsigned char) 257); would be undefined behavior - `char' is usually signed + // on most modern systems, and signed integer overflow invokes UB. + // Also, for determining the maximal value of a `char`, a `signed char` and an `unisigned char`, + // respectively, use the CHAR_MAX, SCHAR_MAX and UCHAR_MAX macros from <limits.h> + + // Integral types can be cast to floating-point types, and vice-versa. + printf("%f\n", (float)100); // %f formats a float + printf("%lf\n", (double)100); // %lf formats a double + printf("%d\n", (char)100.0); + + /////////////////////////////////////// + // Pointers + /////////////////////////////////////// + + // A pointer is a variable declared to store a memory address. Its declaration will + // also tell you the type of data it points to. You can retrieve the memory address + // of your variables, then mess with them. + + int x = 0; + printf("%p\n", (void *)&x); // Use & to retrieve the address of a variable + // (%p formats an object pointer of type void *) + // => Prints some address in memory; + + + // Pointers start with * in their declaration + int *px, not_a_pointer; // px is a pointer to an int + px = &x; // Stores the address of x in px + printf("%p\n", (void *)px); // => Prints some address in memory + printf("%zu, %zu\n", sizeof(px), sizeof(not_a_pointer)); + // => Prints "8, 4" on a typical 64-bit system + + // To retreive the value at the address a pointer is pointing to, + // put * in front to de-reference it. + // Note: yes, it may be confusing that '*' is used for _both_ declaring a pointer and dereferencing it. + printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of + + // 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 + printf("%d\n", *px); // => Prints 1 + printf("%d\n", x); // => Prints 1 + + int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory + int xx; + for (xx = 0; xx < 20; xx++) { + 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). + // This works because arrays often decay into pointers to their first element. + // For example, when an array is passed to a function or is assigned to a pointer, + // 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). + // 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 + } // 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) + // 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 /////////////////////////////////////// @@ -300,7 +396,8 @@ function_1(); // Function declaration syntax: // <return type> <function name>(<args>) -int add_two_ints(int x1, int x2){ +int add_two_ints(int x1, int x2) +{ return x1 + x2; // Use return to return a value } @@ -312,10 +409,12 @@ Example: in-place string reversal */ // A void function returns no value -void str_reverse(char* str_in){ +void str_reverse(char *str_in) +{ char tmp; - int ii=0, len = strlen(str_in); // Strlen is part of the c standard library - for(ii=0; ii<len/2; ii++){ + int ii = 0; + size_t len = strlen(str_in); // `strlen()` is part of the c standard library + for (ii = 0; ii < len / 2; ii++) { tmp = str_in[ii]; str_in[ii] = str_in[len - ii - 1]; // ii-th char from end str_in[len - ii - 1] = tmp; @@ -336,15 +435,20 @@ printf("%s\n", c); // => ".tset a si sihT" typedef int my_type; my_type my_type_var = 0; -// Structs are just collections of data +// 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. -void function_1(){ - +void function_1() +{ struct rectangle my_rec; // Access struct members with . @@ -352,22 +456,29 @@ void function_1(){ my_rec.height = 20; // You can declare pointers to structs - struct rectangle* my_rec_ptr = &my_rec; + struct rectangle *my_rec_ptr = &my_rec; // Use dereferencing to set struct pointer members... (*my_rec_ptr).width = 30; - // ... or use the -> shorthand + // ... or even better: prefer the -> shorthand for the sake of readability my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10; } // You can apply a typedef to a struct for convenience typedef struct rectangle rect; -int area(rect r){ +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: +int area(const rect *r) +{ + return r->width * r->height; +} + /////////////////////////////////////// // Function pointers /////////////////////////////////////// @@ -379,10 +490,11 @@ However, definition syntax may be initially confusing. Example: use str_reverse from a pointer */ -void str_reverse_through_pointer(char * str_in) { +void str_reverse_through_pointer(char *str_in) { // Define a function pointer variable, named f. void (*f)(char *); // Signature should exactly match the target function. f = &str_reverse; // Assign the address for the actual function (determined at runtime) + // f = str_reverse; would work as well - functions decay into pointers, similar to arrays (*f)(str_in); // Just calling the function through the pointer // f(str_in); // That's an alternative but equally valid syntax for calling it. } @@ -403,7 +515,15 @@ typedef void (*my_fnp_type)(char *); ## Further Reading Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language) +It is *the* book about C, written by the creators of C. Be careful, though - it's ancient and it contains some +inaccuracies (well, ideas that are not considered good anymore) or now-changed practices. + +Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/). + +If you have a question, read the [compl.lang.c Frequently Asked Questions](http://c-faq.com). -Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/) +It's very important to use proper spacing, indentation and to be consistent with your coding style in general. +Readable code is better than clever code and fast code. For a good, sane coding style to adopt, see the +[Linux kernel coding stlye](https://www.kernel.org/doc/Documentation/CodingStyle). Other than that, Google is your friend. diff --git a/fr-fr/ruby-fr.html.markdown b/fr-fr/ruby-fr.html.markdown new file mode 100644 index 00000000..5efb2f3c --- /dev/null +++ b/fr-fr/ruby-fr.html.markdown @@ -0,0 +1,407 @@ +--- +language: ruby +filename: learnruby-fr.rb +contributors: + - ["David Underwood", "http://theflyingdeveloper.com"] + - ["Joel Walden", "http://joelwalden.net"] + - ["Luke Holder", "http://twitter.com/lukeholder"] + - ["Tristan Hume", "http://thume.ca/"] + - ["Nick LaMuro", "https://github.com/NickLaMuro"] +translators: + - ["Geoffrey Roguelon", "https://github.com/GRoguelon"] + - ["Nami-Doc", "https://github.com/Nami-Doc"] +lang: fr-fr +--- + +```ruby +# Ceci est un commentaire + +=begin +Ceci est un commentaire multiligne +Personne ne les utilise +Vous devriez en faire de même +=end + +# Tout d'abord : Tout est un objet. + +# Les nombres sont des objets + +3.class #=> Fixnum + +3.to_s #=> "3" + +# Les opérateurs de base +1 + 1 #=> 2 +8 - 1 #=> 7 +10 * 2 #=> 20 +35 / 5 #=> 7 + +# Les opérateurs sont juste des raccourcis +# pour appeler une méthode sur un objet +1.+(3) #=> 4 +10.* 5 #=> 50 + +# Les valeurs spéciales sont des objets +nil # Nul +true # Vrai +false # Faux + +nil.class #=> NilClass +true.class #=> TrueClass +false.class #=> FalseClass + +# Égalité +1 == 1 #=> true +2 == 1 #=> false + +# Inégalité +1 != 1 #=> false +2 != 1 #=> true +!true #=> false +!false #=> true + +# à part false lui-même, nil est la seule autre valeur 'false' + +!nil #=> true +!false #=> true +!0 #=> false + +# Plus de comparaisons +1 < 10 #=> true +1 > 10 #=> false +2 <= 2 #=> true +2 >= 2 #=> true + +# Les chaînes de caractères sont des objets + +'Je suis une chaîne de caractères'.class #=> String +"Je suis également une chaîne de caractères".class #=> String + +placeholder = "utiliser l'interpolation de chaîne de caractères" +"Je peux #{placeholder} quand j'utilise les guillemets" +#=> "Je peux utiliser l'interpolation de chaîne de caractères quand j'utilise les guillemets" + +# Affichez un message +puts "J'affiche à l'écran!" + +# Variables +x = 25 #=> 25 +x #=> 25 + +# Notez que l'affectation retourne la valeur affectée. +# Cela signifie que vous pouvez affecter plusieurs fois de suite : + +x = y = 10 #=> 10 +x #=> 10 +y #=> 10 + +# Par convention, utilisez la notation underscore +# pour nommer les variables +snake_case = true + +# Utilisez des noms de variable explicites +path_to_project_root = '/nom/correct/' +path = '/mauvais/nom/' + +# Symboles (aussi des objets) +# Les symboles sont immuables, constants, +# réutilisables et représentés en interne +# par une valeur entière. Ils sont souvent +# utilisés à la place des chaînes de caractères +# pour transmettre efficacement des valeurs +# spécifiques ou significatives + +:pending.class #=> Symbol + +status = :pending + +status == :pending #=> true + +status == 'pending' #=> false + +status == :approved #=> false + +# Tableaux + +# Ceci est un tableau +array = [1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5] + +# Les tableaux contiennent différents types d'élément. + +[1, "hello", false] #=> [1, "hello", false] + +# Les tableaux peuvent être indexés +# Du début +array[0] #=> 1 +array[12] #=> nil + +# Comme les opérateurs, la syntaxe [var] est juste un raccourci +# pour appeler la méthode [] d'un objet +array.[] 0 #=> 1 +array.[] 12 #=> nil + +# Depuis la fin +array[-1] #=> 5 + +# Avec un index de début et de fin +array[2, 4] #=> [3, 4, 5] + +# Ou avec un intervalle +array[1..3] #=> [2, 3, 4] + +# Ajoutez un élément au tableau comme ceci +array << 6 #=> [1, 2, 3, 4, 5, 6] + +# Les Hash sont des dictionnaires Ruby contenant des paires de clé/valeur. +# Les Hash sont délimitées par des accolades : +hash = {'color' => 'green', 'number' => 5} + +hash.keys #=> ['color', 'number'] + +# Les Hash retournent la valeur +# en utilisant la clé associée à la valeur : +hash['color'] #=> 'green' +hash['number'] #=> 5 + +# Recherchez une clé inexistante dans une Hash retourne nil : +hash['nothing here'] #=> nil + +# Depuis Ruby 1.9, Une syntaxe spécifique est apparue en utilisant les symboles comme clés : + +new_hash = { defcon: 3, action: true} + +new_hash.keys #=> [:defcon, :action] + +# Astuce : Les tableaux et les Hash sont dénombrables +# Ils partagent un certain nombre de méthodes pratiques +# telle que each, map, count, etc... + +# Structures de contrôle + +if true + "si instruction" +elsif false + "autrement si, facultatif" +else + "autrement, également facultatif" +end + +for compteur in 1..5 + puts "itération #{compteur}" +end +#=> itération 1 +#=> itération 2 +#=> itération 3 +#=> itération 4 +#=> itération 5 + +# CEPENDANT, l'usage de la boucle for est très rare. +# À la place, utilisez la méthode "each" +# et passez lui un bloc de code. +# Un bloc de code est un ensemble d'instructions que vous pouvez passer à une methode comme "each". +# Les blocs sont similaires aux lambdas, les fonctions anonymes ou les closures dans d'autres langages. +# +# La méthode "each" exécute le bloc de code pour chaque élément de l'intervalle d'éléments. +# Le bloc de code passe un paramètre compteur. +# Appelez la méthode "each" avec un bloc de code comme ceci : + +(1..5).each do |compteur| + puts "itération #{compteur}" +end +#=> itération 1 +#=> itération 2 +#=> itération 3 +#=> itération 4 +#=> itération 5 + +# Vous pouvez également mettre un bloc de code entre accolades : +(1..5).each {|compteur| puts "itération #{compteur}"} + +# Le contenu des structures de données peut être parcouru +# en utilisant la méthode each. +array.each do |element| + puts "#{element} est une partie du tableau" +end +hash.each do |cle, valeur| + puts "#{cle} est #{valeur}" +end + +compteur = 1 +while compteur <= 5 do + puts "itération #{compteur}" + compteur += 1 +end +#=> itération 1 +#=> itération 2 +#=> itération 3 +#=> itération 4 +#=> itération 5 + +grade = 'B' + +case grade +when 'A' + puts "Excellent" +when 'B' + puts "Plus de chance la prochaine fois" +when 'C' + puts "Vous pouvez faire mieux" +when 'D' + puts "C'est pas terrible" +when 'F' + puts "Vous avez échoué!" +else + puts "Sytème de notation alternatif" +end + +# Fonctions + +def double(x) + x * 2 +end + +# Les fonctions (et tous les blocs de code) retournent +# implicitement la valeur de la dernière instruction évaluée +double(2) #=> 4 + +# Les paranthèses sont facultative +# lorsqu'il n'y a pas d'ambiguïté sur le résultat +double 3 #=> 6 + +double double 3 #=> 12 + +def sum(x,y) + x + y +end + +# Les paramètres de méthode sont séparés par des virgules +sum 3, 4 #=> 7 + +sum sum(3,4), 5 #=> 12 + +# yield +# Toutes les méthodes ont un argument facultatif et implicite +# de type bloc de code +# il peut être appelé avec le mot clé 'yield' + +def surround + puts "{" + yield + puts "}" +end + +surround { puts 'Bonjour tout le monde' } + +# { +# Bonjour tout le monde +# } + + +# Définissez une classe avec le mot clé 'class' +class Humain + + # Une variable de classe + # est partagée par toutes les instances de cette classe. + @@espece = "H. sapiens" + + # Constructeur de classe + def initialize(nom, age = 0) + # Affectez l'argument à la variable d'instance 'nom' + # pour la durée de vie de l'instance de cette classe + @nom = nom + # Si le paramètre 'age' est absent, + # la valeur par défaut définie dans la liste des arguments sera utilisée. + @age = age + end + + # Une simple méthode setter + def nom=(nom) + @nom = nom + end + + # Une simple méthode getter + def nom + @nom + end + + # Une méthode de classe utilise le mot clé 'self' + # pour se distinguer de la méthode d'instance. + # La méthode sera alors accessible à partir de la classe + # et non pas de l'instance. + def self.say(msg) + puts "#{msg}" + end + + def species + @@species + end + +end + + +# Instanciez une classe +jim = Humain.new("Jim Halpert") + +dwight = Humain.new("Dwight K. Schrute") + +# Appelez quelques méthodes +jim.espece #=> "H. sapiens" +jim.nom #=> "Jim Halpert" +jim.nom = "Jim Halpert II" #=> "Jim Halpert II" +jim.nom #=> "Jim Halpert II" +dwight.espece #=> "H. sapiens" +dwight.nom #=> "Dwight K. Schrute" + +# Appelez la méthode de classe +Humain.say("Hi") #=> "Hi" + +# Les classes sont également des objets en Ruby. +# Par conséquent, les classes peuvent avoir des variables d'instance. +# Les variables de classe sont partagées parmi +# la classe et ses descendants. + +# Classe parente +class Humain + @@foo = 0 + + def self.foo + @@foo + end + + def self.foo=(valeur) + @@foo = valeur + end +end + +# Classe fille +class Travailleur < Humain +end + +Humain.foo # 0 +Travailleur.foo # 0 + +Humain.foo = 2 # 2 +Travailleur.foo # 2 + +# Les variables d'instance de classe ne sont pas partagées +# avec les classes héritées. + +class Humain + @bar = 0 + + def self.bar + @bar + end + + def self.bar=(valeur) + @bar = valeur + end +end + +class Docteur < Humain +end + +Humain.bar # 0 +Docteur.bar # nil + +``` diff --git a/ruby.html.markdown b/ruby.html.markdown index 19f2ec86..3a233d98 100644 --- a/ruby.html.markdown +++ b/ruby.html.markdown @@ -36,7 +36,7 @@ You shouldn't either # Arithmetic is just syntactic sugar # for calling a method on an object 1.+(3) #=> 4 -10.* 5 #=> 50 +10.* 5 #=> 50 # Special values are objects nil # Nothing to see here @@ -242,7 +242,7 @@ when 'D' puts "Scraping through" when 'F' puts "You failed!" -else +else puts "Alternative grading system, eh?" end @@ -252,7 +252,7 @@ def double(x) x * 2 end -# Functions (and all blocks) implcitly return the value of the last statement +# Functions (and all blocks) implicitly return the value of the last statement double(2) #=> 4 # Parentheses are optional where the result is unambiguous |