---
name: "memcpy"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/memcpy"
---

# memcpy(3)

memory copy

## NAME

memcpy - memory copy

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <string.h>  // see memory.h(3head)
```

**void \*memcpy(**size\_t n;              **void** *dest***\[restrict** *n***\], const void** *src***\[restrict** *n***\],**              **size\_t** *n***);**

## DESCRIPTION

The **memcpy**() function copies *n* bytes from memory area *src* to memory area *dest*. The memory areas must not overlap. Use [**memmove**(3)](/memmove/3.md) if the memory areas do overlap.

## RETURN VALUE

The **memcpy**() function returns a pointer to *dest*.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **memcpy**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

POSIX.1-2001, C89, SVr4, 4.3BSD.

## CAVEATS

Failure to observe the requirement that the memory areas do not overlap has been the source of significant bugs. (POSIX and the C standards are explicit that employing **memcpy**() with overlapping areas produces undefined behavior.) Most notably, in glibc 2.13 a performance optimization of **memcpy**() on some platforms (including x86-64) included changing the order in which bytes were copied from *src* to *dest*.

This change revealed breakages in a number of applications that performed copying with overlapping areas. Under the previous implementation, the order in which the bytes were copied had fortuitously hidden the bug, which was revealed when the copying order was reversed. In glibc 2.14, a versioned symbol was added so that old binaries (i.e., those linked against glibc versions earlier than 2.14) employed a **memcpy**() implementation that safely handles the overlapping buffers case (by providing an "older" **memcpy**() implementation that was aliased to [**memmove**(3)](/memmove/3.md)).

## SEE ALSO

[**memory.h**(3head)](/memory.h/3head.md), [**memmove**(3)](/memmove/3.md), [**mempcpy**(3)](/mempcpy/3.md), [**wmemcpy**(3)](/wmemcpy/3.md)