realloc
Defined in header
<stdlib.h>
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void *realloc( void *ptr, size_t new_size );
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Reallocates the given area of memory. It must be previously allocated by malloc(), calloc() or realloc()
and not yet freed with free, otherwise, the results are undefined.
The reallocation is done by either:
ptr
, if possible. The contents of the area remain unchanged up to the lesser of the new and old sizes. If the area is expanded, the contents of the new part of the array are undefined. new_size
bytes, copying memory area with size equal the lesser of the new and the old sizes, and freeing the old block.If there is not enough memory, the old memory block is not freed and null-pointer is returned.
If ptr
is NULL, the behavior is the same as calling malloc(new_size
).
If new_size
is zero, the behavior is implementation defined (null pointer may be returned, or some non-null pointer may be returned that may not be used to access storage).
A previous call to free or |
(since C11) |
Contents |
[edit] Parameters
ptr | - | pointer to the memory area to be reallocated |
new_size | - | new size of the array |
[edit] Return value
Pointer to the beginning of newly allocated memory or NULL if an error has occurred. The pointer must be deallocated with free().
[edit] Example
This section is incomplete Reason: simplify or make more practical |
#include <stdio.h> #include <stdlib.h> int main(void) { /* Allocate array A with 6 integers. */ int* pa = realloc(NULL, 6*sizeof(int)); if (!pa) { /* if realloc() fails, terminate program */ printf("realloc() failed in file %s at line %d\n", __FILE__,__LINE__); printf("*** PROGRAM TERMINATED *** \n"); exit(1); } printf("starting address of pa: %p\n", (void*)pa); /* Allocate a single integer to provide a barrier to an expansion of pa. */ int* pb = malloc(1 * sizeof(int)); if (!pb) { /* if malloc() fails, terminate program */ printf("malloc() failed in file %s at line %d\n", __FILE__,__LINE__); printf("*** PROGRAM TERMINATED *** \n"); exit(1); } /* The starting address of array A changes because there is insufficient */ /* room to expand A from 6 to 7 integers. */ pa = realloc(pa, 7*sizeof(int)); if (!pa) { /* if realloc() fails, terminate program */ printf("realloc() failed in file %s at line %d\n", __FILE__,__LINE__); printf("*** PROGRAM TERMINATED *** \n"); exit(1); } printf("starting address of pa: %p\n", (void*)pa); free(pa); free(pb); return 0; }
Possible output:
starting address of pa: 0x1f82010 starting address of pa: 0x1f82050
[edit] See also
C++ documentation for realloc
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