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# std::memmove

From cppreference.com
< cpp‎ | string‎ | byte

Defined in header `<cstring>` |  |
void* memmove( void* dest, const void* src, std::size_t count ); |  |

Copies `count` characters from the object pointed to by `src` to the object pointed to by `dest`. Both objects are reinterpreted as arrays of unsigned char.

The objects may overlap: copying takes place as if the characters were copied to a temporary character array and then the characters were copied from the array to `dest`.

If the objects are not `TriviallyCopyable`, the behavior of `memmove` is not specified and may be undefined.

### [edit] Parameters

dest | - | pointer to the memory location to copy to
src | - | pointer to the memory location to copy from
count | - | number of bytes to copy

### [edit] Return value

`dest`

### [edit] Notes

Despite being specified "as if" a temporary buffer is used, actual implementations of this function do not incur the overhead of double copying or extra memory. For small count, it may load up and write out registers; for larger blocks, a common approach (glibc and bsd libc) is to copy bytes forwards from the beginning of the buffer if the destination starts before the source, and backwards from the end otherwise, with a fall back to std::memcpy when there is no overlap at all.

### [edit] Example

Run this code

    #include <iostream>
    #include <cstring>

    int main()
    {
        char str[] = "1234567890";
        std::cout << str << '\n';
        std::memmove(str + 4, str + 3, 3); // copies from [4, 5, 6] to [5, 6, 7]
        std::cout << str << '\n';
    }

Output:

    1234567890
    1234456890

### [edit] See also

memcpy | copies one buffer to another (function) [edit]
memset | fills a buffer with a character (function) [edit]
wmemmove | copies a certain amount of wide characters between two, possibly overlapping, arrays (function) [edit]
copycopy_if (C++11) | copies a range of elements to a new location (function template) [edit]
copy_backward | copies a range of elements in backwards order (function template) [edit]
is_trivially_copyable (C++11) | checks if a type is trivially copyable (class template) [edit]
C documentation for memmove

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