new.h
_set_new_handler
- Header
- new.h
- Prototype
- _PNH _set_new_handler(_PNH pNewHandler);
- Description
- The _set_new_handler function defines a handler to be called
when the new operator is unable to allocate a requested amount of
memory from the default heap. The _set_fnew_handler function
establishes a new handler for the far heap; _set_nnew_handler
establishes a new handler for the near heap.
The _set_new_handler function automatically maps to either the _set_fnew_handler or _set_nnew_handler, depending on the default data model.
For all of the _set_new_handler functions, the pNewHandler argument is a pointer to the function that you write to be called when new fails. This argument is of type _PNH, which is a pointer to a function that returns type int and takes an argument of type size_t. Use size_t to specify the amount of space to allocate.
The _set_new_handler functions provide a garbage collection scheme. The run-time system retries allocation each time your function returns a non-zero value and fails if your function returns 0.
In a multi-threaded environment, handlers are maintained separately for each process and thread. Each new process does not have installed handlers. Each new thread receives a copy of its parent thread's new handlers. Therefore, each process and thread must manage its own free-store error handling.
- Synonym
- Function: set_new_handler
- Return Value
- Returns a pointer to the previous new handler function. There is no error return.
- Compatibility
- DOS Windows 3.x Phar Lap DOSX Win32
- See Also
- malloc calloc realloc Functions free
- Example
/* Example of _set_new_handler */ #include <stdlib.h> #include <stdio.h> #include <new.h> #define MEMSIZE 1024 #define ZONESIZE MEMSIZE * 4 /* This is the safety zone. If this is eaten into, then memory is low */ char *zone = new char[ZONESIZE]; char *forprintf = new char[128]; /* This handler will free the safety zone when there is an allocation error. It won't bother if the alloction request is too big for the zone. */ int zone_handler(size_t alocsize) { if (alocsize > ZONESIZE) { delete forprintf; printf("\nThat's it, now you've used up all the memory.\n"); return 0; } if (zone) { delete zone; zone = NULL; printf("\nWARNING: Memory is low, they have taken the zone!\n"); return 1; } delete forprintf; printf("\nThat's it, now you've used up all the memory.\n"); return 0; } void main() { char *waste; unsigned long int total_wasted = 0; _set_new_handler (zone_handler); printf("Wasting memory...\n"); do { printf("\rWasting %u", total_wasted); waste = new char[MEMSIZE]; total_wasted += MEMSIZE; } while (waste); }- Output
Wasting memory... Wasting 46080 WARNING: Memory is low, they have taken the zone! Wasting 49152 That's it, now you've used up all the memory.