# std::malloc

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< cpp‎ | memory‎ | c

Defined in header `<cstdlib>` |  |
void* malloc( std::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 scalar 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, but has to be passed to std::free)

The following functions are required to be thread-safe:

- The library versions of `operator new` and `operator delete`
- User replacement versions of global `operator new` and `operator delete`
- std::calloc, std::malloc, std::realloc , std::aligned_alloc (since C++17), std::free

Calls to these functions that allocate or deallocate a particular unit of storage occur in a single total order, and each such deallocation call happens-before the next allocation (if any) in this order.

(since C++11)

### 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 std::free() or `std::realloc()`.

On failure, returns a null pointer.

### Notes

This function does not call constructors or initialize memory in any way. There are no ready-to-use smart pointers that could guarantee that the matching deallocation function is called. The preferred method of memory allocation in C++ is using RAII-ready functions std::make_unique, std::make_shared, container constructors, etc, and, in low-level library code, new-expression.

### Example

Run this code

    #include <iostream>
    #include <cstdlib>
    #include <string>

    int main()
    {
        // allocates enough for an array of 4 strings
        if(auto p = (std::string*)std::malloc(4 * sizeof(std::string)))
        {
            int i = 0;
            try
            {
                for(; i != 4; ++i) // populate the array
                    new(p + i) std::string(5, 'a' + i);

                for(int j = 0; j != 4; ++j) // print it back out
                    std::cout << "p[" << j << "] == " << p[j] << '\n';
            }
            catch(...) {}

            for(; i != 0; --i) // clean up
                p[i - 1].~basic_string();

            std::free(p);
        }
    }

Output:

    p[0] == aaaaa
    p[1] == bbbbb
    p[2] == ccccc
    p[3] == ddddd

### See also

operator newoperator new[] | allocation functions (function)
get_temporary_buffer (deprecated in C++17)(removed in C++20) | obtains uninitialized storage (function template)

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