Reallocate memory blocks.
| #include <stdlib.h> | For ANSI compatibility (realloc only) | |
| #include <malloc.h> | Required only for function declarations |
void *realloc( void *memblock, size_t size );
void __based( void ) *_brealloc( __segment seg,
void __based( void ) *memblock, size_t size );
void __far *_frealloc( void __far *memblock, size_t size );
void __near *_nrealloc( void __near *memblock, size_t size );
| memblock | Pointer to previously allocated memory block | |
| size | New size in bytes | |
| seg | Segment selector |
The realloc family of functions changes the size of a previously allocated memory block. The memblock argument points to the beginning of the memory block. If memblock is NULL (_NULLOFF for _brealloc), realloc functions in the same way as malloc and allocates a new block of size bytes. If memblock is not NULL (_NULLOFF for _brealloc), it should be a pointer returned by a prior call to calloc, malloc, or realloc.
The size argument gives the new size of the block, in bytes. The contents of the block are unchanged up to the shorter of the new and old sizes, although the new block may be in a different location.
In large data models (that is, compact-, large-, and huge-model programs), realloc maps to _frealloc. In small data models (tiny-, small-, and medium-model programs), realloc maps to _nrealloc.
The various realloc functions reallocate memory in the heap as specified in the following list:
| Function | Heap |
| realloc | Depends on data model of program |
| _brealloc | Based heap specified by seg value |
| _frealloc | Far heap (outside default data segment) |
| _nrealloc | Near heap (inside default data segment) |
The realloc functions return a void pointer to the reallocated (and possibly moved) memory block.
The return value is NULL (_NULLOFF for _brealloc) if the size is zero and the buffer argument is not NULL (_NULLOFF for _brealloc), or if there is not enough available memory to expand the block to the given size. In the first case, the original block is freed. In the second, the original block is unchanged.
The storage space pointed to by the return value is guaranteed to be suitably aligned for storage of any type of object. To get a pointer to a type other than void, use a type cast on the return value.
realloc
Standards:ANSI, UNIX
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
_brealloc, _frealloc, _nrealloc
Standards:None
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:None
calloc functions, free functions, malloc functions
/* REALLOC.C: This program allocates a block of memory for buffer
* and then uses _msize to display the size of that block. Next, it
* uses realloc to expand the amount of memory used by buffer
* and then calls _msize again to display the new amount of
* memory allocated to buffer.
*/
#include <stdio.h>
#include <malloc.h>
#include <stdlib.h>
void main( void )
{
long *buffer;
size_t size;
if( (buffer = (long *)malloc( 1000 * sizeof( long ) )) == NULL )
exit( 1 );
size = _msize( buffer );
printf( “Size of block after malloc of 1000 longs: %u\n”, size );
/* Reallocate and show new size: */
if( (buffer = realloc( buffer, size + (1000 * sizeof( long )) )) == NULL )
exit( 1 );
size = _msize( buffer );
printf( “Size of block after realloc of 1000 more longs: %u\n”, size );
free( buffer );
exit( 0 );
}
Size of block after malloc of 1000 longs: 4000
Size of block after realloc of 1000 more longs: 8000