wmemmove, wmemmove_s

Defined in header <wchar.h>
wchar_t* wmemmove( wchar_t* dest, const wchar_t* src, size_t count );
(1) (since C95)
errno_t wmemmove_s( wchar_t *dest, rsize_t destsz,
                    const wchar_t *src, rsize_t count);
(2) (since C11)
1) Copies exactly count successive wide characters from the wide character array pointed to by src to the wide character array pointed to by dest. If count is zero, the function does nothing. The arrays may overlap: copying takes place as if the wide characters were copied to a temporary wide character array and then copied from the temporary array to dest.
2) Same as (1), except that the following errors are detected at runtime and call the currently installed constraint handler function:
  • src or dest is a null pointer
  • destsz or count is greater than RSIZE_MAX/sizeof(wchar_t)
  • count is greater than destsz (overflow would occur)
As with all bounds-checked functions, wmemcpy_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <wchar.h>.


dest - pointer to the wide character array to copy to
src - pointer to the wide character array to copy from
destsz - max number of wide characters to write (the size of the destination buffer)
count - number of wide characters to copy

Return value

1) Returns a copy of dest
2) Returns zero on success, returns non-zero on error. Also, on error, fills the entire dst up to and not including dst+dstsz with null wide characters, L'\0' (unless dest is null or destsz is greater than RSIZE_MAX/sizeof(wchar_t))


This function is not locale-sensitive and pays no attention to the values of the wchar_t objects it copies: nulls as well as invalid characters are copied too.


#include <stdio.h>
#include <wchar.h>
#include <locale.h>
int main(void)
    setlocale(LC_ALL, "en_US.utf8");
    wchar_t str[] = L"αβγδεζηθικλμνξοπρστυφχψω";
    printf("%ls\n", str);
    wmemmove(str+4, str+3, 3); // copy from [δεζ] to [εζη]
    printf("%ls\n", str);




  • C11 standard (ISO/IEC 9899:2011):
    • The wmemmove function (p: 432)
    • K. The wmemmove_s function (p: 642)
  • C99 standard (ISO/IEC 9899:1999):
    • The wmemmove function (p: 378)

See also

moves one buffer to another
copies a certain amount of wide characters between two non-overlapping arrays
C++ documentation for wmemmove

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