| Standards / Extensions | C or C++ | Dependencies |
|---|---|---|
ISO C |
both |
#include <stdlib.h>
void *realloc(void *ptr, size_t size);Changes the size of a previously reserved storage block. The ptr argument points to the beginning of the block. 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.
If the ptr is NULL, realloc() reserves a block of storage of size bytes. It does not give all bits of each element an initial value of 0.
If size is 0 and ptr is not NULL, the storage pointed to by ptr is freed and NULL is returned.
If you use realloc() with a pointer that does not point to a ptr created previously by malloc(), calloc(), or realloc(), or if you pass ptr to storage already freed, you get undefined behavior—usually an exception.
If you ask for more storage, the contents of the extension are undefined and are not guaranteed to be 0.
The storage to which the returned value points is aligned for storage of any type of object. Under z/OS® XL C only, if 4K alignment is required, the __4kmalc() function should be used. (This function is only available to C applications in stand-alone System Programming C (SPC) Facility applications.) The library functions specific to the System Programming C (SPC) environment are described in z/OS XL C/C++ Programming Guide.
To investigate the cause of realloc() running out of heap storage, see z/OS Language Environment Programming Reference
Special behavior for C++: The C++ keywords new and delete are not interoperable with calloc(), free(), malloc(), or realloc().
If successful, realloc() returns a pointer to the reallocated storage block. The storage location of the block might be moved. Thus, the returned value is not necessarily the same as the ptr argument to realloc().
⁄* CELEBR06
This example allocates storage for the prompted size of array
and then uses &realloc. to reallocate the block to hold the
new size of the array.
The contents of the array are printed after each allocation.
*⁄
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
long * array; ⁄* start of the array *⁄
long * ptr; ⁄* pointer to array *⁄
int i; ⁄* index variable *⁄
int num1, num2; ⁄* number of entries of the array *⁄
void print_array( long *ptr_array, int size);
printf( "Enter the size of the array\n" );
scanf( "%i", &num1 );
⁄* allocate num1 entries using malloc() *⁄
if ( (array = (long *)malloc( num1 * sizeof( long ))) != NULL ) {
for ( ptr = array, i = 0; i < num1 ; ++i ) ⁄* assign values *⁄
*ptr++ = i;
print_array( array, num1 );
printf("\n");
}
else { ⁄* malloc error *⁄
printf( "Out of storage\n" );
abort();
}
⁄* Change the size of the array ... *⁄
printf( "Enter the size of the new array\n" );
scanf( "%i", &num2);
if ( (array = (long *)realloc( array, num2* sizeof( long ))) != NULL )
{
for ( ptr = array + num1, i = num1; i <= num2; ++i )
*ptr++ = i + 2000; ⁄* assign values to new elements *⁄
print_array( array, num2 );
}
else { ⁄* realloc error *⁄
printf( "Out of storage\n" );
abort();
}
}
void print_array( long * ptr_array, int size )
{
int i;
long * index = ptr_array;
printf("The array of size %d is:\n", size);
for ( i = 0; i < size; ++i ) ⁄* print the array out *⁄
printf( " array[ %i ] = %li\n", i, ptr_array[i] );
} Enter the size of the array
The array of size 2 is:
array[ 0 ] = 0
array[ 1 ] = 1
Enter the size of the new array
The array of size 4 is:
array[ 0 ] = 0
array[ 1 ] = 1
array[ 2 ] = 2002
array[ 3 ] = 2003