From cppreference.com
void*memmove(void*dest,constvoid*src,std::size_tcount);Performs the following operations in order:
Copies count characters (as if of type unsignedchar, the same below) from the object pointed to by src into a temporary array arr of count characters, where arr does not overlap the objects pointed to by dest and src.
objects at dest.
Copies count characters from arr into the object pointed to by dest.
If dest or src is a
or
, the behavior is undefined.
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 Return value
If there is a
, returns a pointer to it; otherwise returns dest.
Notes
Despite the specification says 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
when there is no overlap at all.
Where
prohibits examining the same memory as values of two different types, std::memmove may be used to convert the values.
Example
Run this code
#include<cstring>#include<iostream>intmain(){charstr[]="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 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 it was unclear whether the returned pointer points to a suitable created object made clear See also
copies one buffer to another
(function)
(C++26)
fills a buffer with a character
(function)
copies a certain amount of wide characters between two, possibly overlapping, arrays
(function)
(C++11)
copies a range of elements to a new location
(function template & algorithm function object)
(C++20)(C++20)
copies a range of elements in backwards order
(function template & algorithm function object)
(C++20)
(C++11)
checks if a type is trivially copyable
(class template)
for memmove