Defined in header <stdlib.h> | ||
Allocates memory for an array ofnum objects ofsize and initializes all bytes in the allocated storage to zero.
If allocation succeeds, returns a pointer to the lowest (first) byte in the allocated memory block that is suitably aligned for any object type withfundamental alignment.
Ifsize 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 tofree,free_sized, andfree_aligned_sized(since C23) orrealloc that deallocates a region of memorysynchronizes-with a call to | (since C11) |
Contents |
| num | - | number of objects |
| size | - | size of each object |
On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated withfree() orrealloc().
On failure, returns a null pointer.
Due to the alignment requirements, the number of allocated bytes is not necessarily equal tonum* size.
Initialization to all bits zero does not guarantee that a floating-point or a pointer would be initialized to0.0 and the null pointer value, respectively (although that is true on all common platforms).
Originally (in C89), support for zero size was added to accommodate code such as
OBJ* p= calloc(0,sizeof(OBJ));// "zero-length" placeholder...while(1){ p=realloc(p, c*sizeof(OBJ));// reallocations until size settles ...// code that may change c or break out of loop}
#include <stdio.h>#include <stdlib.h> int main(void){int* p1= calloc(4,sizeof(int));// allocate and zero out an array of 4 intint* p2= calloc(1,sizeof(int[4]));// same, naming the array type directlyint* p3= calloc(4,sizeof*p3);// same, without repeating the type name if(p2){for(int n=0; n<4;++n)// print the arrayprintf("p2[%d] == %d\n", n, p2[n]);} free(p1);free(p2);free(p3);}
Output:
p2[0] == 0p2[1] == 0p2[2] == 0p2[3] == 0
C++ documentation forcalloc |
