# malloc

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< c‎ | memory

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

Allocates `size` bytes of uninitialized storage.

If allocation succeeds, returns a pointer that is suitably aligned for any object type with fundamental alignment.

If `size` is zero, the behavior of `malloc` is implementation-defined. For example, a null pointer may be returned. Alternatively, a non-null pointer may be returned; but such a pointer should not be dereferenced, and should be passed to free to avoid memory leaks.

`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`. There is a single total order of all allocation and deallocation functions operating on each particular region of memory. | (since C11)

### Parameters

size | - | number of bytes to allocate

### Return value

On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated with free() or realloc().

On failure, returns a null pointer.

### Example

Run this code

    #include <stdio.h>
    #include <stdlib.h>

    int main(void)
    {
        int *p1 = malloc(4*sizeof(int));  // allocates enough for an array of 4 int
        int *p2 = malloc(sizeof(int[4])); // same, naming the type directly
        int *p3 = malloc(4*sizeof *p3);   // same, without repeating the type name

        if(p1) {
            for(int n=0; n<4; ++n) // populate the array
                p1[n] = n*n;
            for(int n=0; n<4; ++n) // print it back out
                printf("p1[%d] == %d\n", n, p1[n]);
        }

        free(p1);
        free(p2);
        free(p3);
    }

Output:

    p1[0] == 0
    p1[1] == 1
    p1[2] == 4
    p1[3] == 9

### References

- C17 standard (ISO/IEC 9899:2018):

  - 7.22.3.4 The malloc function (p: 254)

- C11 standard (ISO/IEC 9899:2011):

  - 7.22.3.4 The malloc function (p: 349)

- C99 standard (ISO/IEC 9899:1999):

  - 7.20.3.3 The malloc function (p: 314)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.10.3.3 The malloc function

### See also

free | deallocates previously allocated memory (function)

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