set_constraint_handler_s, constraint_handler_t

 

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Bounds checking

set_constraint_handler_s (C11)

abort_handler_s (C11)

ignore_handler_s (C11)

 

Defined in header <stdlib.h>
constraint_handler_t set_constraint_handler_s( constraint_handler_t handler );	(1)	(since C11)
typedef void (*constraint_handler_t)( const char* restrict msg,                                       void* restrict ptr,                                       errno_t error );	(2)	(since C11)

1) Configures the handler to be called by all bounds-checked functions on a runtime constraint violation or restores the default handler (if handler is a null pointer).

2) The pointer to a handler that will be called on a runtime constraint violation.

If set_constraint_handler_s is never called, the default handler is implementation-defined: it may be abort_handler_s, ignore_handler_s, or some other implementation-defined handler.

As with all bounds-checked functions, set_constraint_handler_s and constraint_handler_t are only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdlib.h>.

Parameters

handler	-	pointer to function of type constraint_handler_t or a null pointer
msg	-	pointer to character string that describes the error
ptr	-	pointer to an implementation-defined object or a null pointer. Examples of implementation-defined objects are objects that give the name of the function that detected the violation and the line number when the violation was detected
error	-	the error about to be returned by the calling function, if it happens to be one of the functions that return errno_t

Return value

A pointer to the previously-installed runtime constraints handler. (Note: this pointer is never a null pointer because calling set_constraint_handler_s(NULL) sets up the system default handler).

Example

Run this code

#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
#ifdef __STDC_LIB_EXT1__
    char dst[2];
    set_constraint_handler_s(ignore_handler_s);
    int r = strcpy_s(dst, sizeof dst, "Too long!");
    printf("dst = \"%s\", r = %d\n", dst, r);
    set_constraint_handler_s(abort_handler_s);
    r = strcpy_s(dst, sizeof dst, "Too long!");
    printf("dst = \"%s\", r = %d\n", dst, r);
#endif
}

Possible output:

dst = "", r = 22
abort_handler_s was called in response to a runtime-constraint violation.
 
The runtime-constraint violation was caused by the following expression in strcpy_s:
(s1max <= (s2_len=strnlen_s(s2, s1max)) ) (in string_s.c:62)
 
Note to end users: This program was terminated as a result
of a bug present in the software. Please reach out to your
software's vendor to get more help.
Aborted

References

• C23 standard (ISO/IEC 9899:2024):

• K.3.6/2 constraint_handler_t (p: TBD)

• K.3.6.1.1 The set_constraint_handler_s function (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• K.3.6/2 constraint_handler_t (p: TBD)

• K.3.6.1.1 The set_constraint_handler_s function (p: TBD)

• C11 standard (ISO/IEC 9899:2011):

• K.3.6/2 constraint_handler_t (p: 604)

• K.3.6.1.1 The set_constraint_handler_s function (p: 604-605)

See also

abort_handler_s (C11)	abort callback for the bounds-checked functions (function)
ignore_handler_s (C11)	ignore callback for the bounds-checked functions (function)