`_CrtSetBreakAlloc`

Article
02/07/2023

Sets a breakpoint on a specified object allocation order number (debug version only).

Syntax

long _CrtSetBreakAlloc(
   long lBreakAlloc
);

Parameters

lBreakAlloc
Allocation order number, for which to set the breakpoint.

Return value

Returns the previous object allocation order number that had a breakpoint set.

Remarks

_CrtSetBreakAlloc allows an application to perform memory leak detection by breaking at a specific point of memory allocation and tracing back to the origin of the request. The function uses the sequential object allocation order number assigned to the memory block when it was allocated in the heap. When _DEBUG isn't defined, calls to _CrtSetBreakAlloc are removed during preprocessing.

The object allocation order number is stored in the lRequest field of the _CrtMemBlockHeader structure, defined in Crtdbg.h. When information about a memory block is reported by one of the debug dump functions, this number is enclosed in braces, such as {36}.

For more information about how _CrtSetBreakAlloc can be used with other memory management functions, see Tracking heap allocation requests. For more information about how memory blocks are allocated, initialized, and managed in the debug version of the base heap, see CRT debug heap details.

Requirements

Routine	Required header
`_CrtSetBreakAlloc`	<crtdbg.h>

For more compatibility information, see Compatibility.

Libraries

Debug versions of C run-time libraries only.

Example

// crt_setbrkal.c
// compile with: -D_DEBUG /MTd -Od -Zi -W3 /c /link -verbose:lib -debug

/*
* In this program, a call is made to the _CrtSetBreakAlloc routine
* to verify that the debugger halts program execution when it reaches
* a specified allocation number.
*/

#include <malloc.h>
#include <crtdbg.h>

int main( )
{
        long allocReqNum;
        char *my_pointer;

        /*
         * Allocate "my_pointer" for the first
         * time and ensure that it gets allocated correctly
         */
        my_pointer = malloc(10);
        _CrtIsMemoryBlock(my_pointer, 10, &allocReqNum, NULL, NULL);

        /*
         * Set a breakpoint on the allocation request
         * number for "my_pointer"
         */
        _CrtSetBreakAlloc(allocReqNum+2);

        /*
         * Alternate freeing and reallocating "my_pointer"
         * to verify that the debugger halts program execution
         * when it reaches the allocation request
         */
        free(my_pointer);
        my_pointer = malloc(10);
        free(my_pointer);
        my_pointer = malloc(10);
        free(my_pointer);
}