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# wmemcpy, wmemcpy_s

From cppreference.com
< c‎ | string‎ | wide

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 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`.

### [edit] 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)

### [edit] 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))

### [edit] 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.

### [edit] Example

Run this code

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

    int main(void)
    {
        wchar_t from1[] = L"नमस्ते";
        size_t sz1 = sizeof from1 / sizeof *from1;
        wchar_t from2[] = L"Բարև";
        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: नमस्ते\0Բարև\0

### [edit] 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)

### [edit] See also

wmemmove wmemmove_s (C95)(C11) | copies a certain amount of wide characters between two, possibly overlapping, arrays (function) [edit]
strncpy strncpy_s (C11) | copies a certain amount of characters from one string to another (function) [edit]
C++ documentation for wmemcpy

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