GCC Extensions for C languages

The GNU compiler (GCC) provides a number of C language extensions that the compiler uses to generate more efficient machine code.

inline functions

Static int foo (void/** /}

Avoid inline

int foo (void/*... ) */ }

Pure function

int foo (int/* /}

The return value is only affected by function arguments or nonvolatile global variables.

Constant function

__ATTRIBUTE__ ((constint foo (int/* ... */ }

The constant function is a strict pure function. The constant function cannot access the global variable, and the parameter cannot be a pointer type. Therefore, the return value of a constant function is only related to the value of the parameter passed by the value.

function with no return value

void foo (int/* ...) */ }

Functions that allocate memory

__attribute__ (mallocvoid *copy (   ) {int);    return malloc (ten);}

Forcing callers to check the return value

1#include <stdio.h>2 3__attribute__ ((Warn_unused_result))intfoo ()4 {5     return 0;6 }7 8 intMain ()9 {Ten foo (); One     return 0; A}

Identify the function as "Deprecated (deprecated)"

void foo (void/*... ) */ }

Identify the function as being used

Static void foo (void/*... ) */ }

Identifies a function or parameter as unused

int foo (int/* ...) */}

Compact Storage (pack) for structures

struct __attribute__ ((packed)) Foo {...};

The packed property tells the compiler that a type or variable should be stored in memory compactly, using as little space as possible, and may not rely on alignment requirements. If you specify this property on a struct (struct) or union (union), you need to store all the variables compactly. If you specify this property only for a variable, only the specific variable is stored compactly.

GCC Extensions for C languages