malloc

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

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Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

Dynamic memory management

malloc

calloc

realloc

free

aligned_alloc (C11)

 

Defined in header <stdlib.h>
void* malloc( size_t size );

Allocates size bytes of uninitialized storage.

If allocation succeeds, returns a pointer to the lowest (first) byte in the allocated memory block that is suitably aligned for any object type.

If 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).

malloc is thread-safe: it behaves as though only accessing the memory locations visible through its argument, and not any static storage. A previous call to free or realloc that deallocates a region of memory synchronizes-with a call to malloc that allocates the same or a part of the same region of memory. This synchronization occurs after any access to the memory by the deallocating function and before any access to the memory by malloc

(since C11)

Parameters

size

-

number of bytes to allocate

Return value

Pointer to the beginning of newly allocated memory or null pointer if error has occurred. The pointer must be deallocated with free().

Example

Run this code

#include <stdio.h>   
#include <stdlib.h> 
 
int main(void) 
{
    /* Allocate an array of four integers. */
    int *pa = malloc(4*sizeof(int));
    if (pa == NULL) {
       printf("malloc() failed in file %s at line # %d", __FILE__,__LINE__);
       exit(1);
    }
 
    /* Initialize array A with values. */
    for (int ndx=0; ndx < 4; ndx++)
        pa[ndx] = ndx;
 
    /* Print one of the array elements. */
    printf("pa[3] = %d\n", pa[3]);
 
    /* Deallocate array pa. */
    free(pa);
    return 0;
}

Output:

pa[3] = 3

See also

C++ documentation for malloc