atexit

int atexit( void (*func)(void) );

Registers the function pointed to by func to be called on normal program termination (via exit() or returning from main()). The functions will be called in reverse order they were registered, i.e. the function registered last will be executed first.

The same function may be registered more than once.

atexit is thread-safe: calling the function from several threads does not induce a data race.

The implementation is guaranteed to support the registration of at least 32 functions. The exact limit is implementation-defined.

Parameters

Return value

​0​ if the registration succeeds, nonzero value otherwise.

Example

#include <stdlib.h>
#include <stdio.h>
 
void f1(void)
{
    puts("f1");
}
 
void f2(void)
{
    puts("f2");
}
 
int main(void)
{
    if ( ! atexit(f1) && ! atexit(f2) && ! atexit(f2) )
        return EXIT_SUCCESS ;
 
    // atexit registration failed
    return EXIT_FAILURE ;
 
}   // <- if registration was successful calls f2, f2, f1

f2
f2
f1

References

• C17 standard (ISO/IEC 9899:2018):
• 7.22.4.2 The atexit function (p: 255)
• C11 standard (ISO/IEC 9899:2011):
• 7.22.4.2 The atexit function (p: 350)
• C99 standard (ISO/IEC 9899:1999):
• 7.20.4.2 The atexit function (p: 315)
• C89/C90 standard (ISO/IEC 9899:1990):
• 4.10.4.2 The atexit function

See also