wmemcpy, wmemcpy_s

Defined in header `<wchar.h>`
	(1)
wchar_t* wmemcpy( wchar_t* dest, const wchar_t* src, size_t count );			(since C95) (until C99)
wchar_t wmemcpy(wchar_t restrict dest, const wchar_t *restrict src, size_t count );			(since C99)
errno_t wmemcpy_s( wchar_t restrict dest, rsize_t destsz, const wchar_t restrict 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 the objects overlap, the behavior is undefined. If count is zero, the function does nothing.

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)
overlap would occur between the source and the destination arrays

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.

Parameters

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

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))

Notes

This function's analog for byte strings is strncpy, not strcpy.

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.

Example

Run this code

#include <stdio.h>
#include <wchar.h>
#include <locale.h>

int main(void)
{
    wchar_t from1[] = L"";
    size_t sz1 = sizeof from1 / sizeof *from1;
    wchar_t from2[] = L"";
    size_t sz2 = sizeof from2 / sizeof *from2;
    wchar_t to[sz1 + sz2];
    wmemcpy(to, from1, sz1); // copy from1, along with its null terminator
    wmemcpy(to + sz1, from2, sz2); // append from2, along with its null terminator

    setlocale(LC_ALL, "en_US.utf8");
    printf("Wide array contains: ");
    for(size_t n = 0; n < sizeof to / sizeof *to; ++n)
        if(to[n])
            printf("%lc", to[n]);
        else
            printf("\\0");
    printf("\n");
}

Possible output:

Wide array contains: \0\0

References

C11 standard (ISO/IEC 9899:2011):

7.29.4.2.3 The wmemcpy function (p: 431)

K.3.9.2.1.3 The wmemcpy_s function (p: 641)

C99 standard (ISO/IEC 9899:1999):

7.24.4.2.3 The wmemcpy function (p: 377)

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