# wcscat, wcscat_s

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< c‎ | string‎ | wide

Defined in header `<wchar.h>` |  |
| (1) |
wchar_t *wcscat( wchar_t *dest, const wchar_t *src ); |  | (since C95) (until C99)
wchar_t *wcscat( wchar_t *restrict dest, const wchar_t *restrict src ); |  | (since C99)
errno_t wcscat_s( wchar_t *restrict dest, rsize_t destsz, const wchar_t *restrict src ); | (2) | (since C11)

1) Appends a copy of the wide string pointed to by `src` to the end of the wide string pointed to by `dest`. The wide character `src[0]` replaces the null terminator at the end of `dest`. The resulting wide string is null-terminated. The behavior is undefined if the destination array is not large enough for the contents of both `str` and `dest` and the terminating null wide character. The behavior is undefined if the strings overlap.
2) Same as (1), except that it may clobber the rest of the destination array (from the last character written to `destsz`) with unspecified values and that the following errors are detected at runtime and call the currently installed constraint handler function:

  - `src` or `dest` is a null pointer
  - `destsz` is zero or greater than RSIZE_MAX/sizeof(wchar_t)
  - there is no null terminator in the first `destsz` wide characters of `dest`
  - truncation would occur (the available space at the end of `dest` would not fit every wide character, including the null terminator, of `src`)
  - overlap would occur between the source and the destination strings
  As with all bounds-checked functions, `wcscat_s` 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 null-terminated wide string to append to
src | - | pointer to the null-terminated wide string to copy from
destsz | - | maximum number of characters to write, typically 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, writes L'\0' to dest[0] (unless `dest` is a null pointer or `destsz` is zero or greater than RSIZE_MAX/sizeof(wchar_t)).

### Example

Run this code

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

    int main(void)
    {
        wchar_t str[50] = L"Земля, прощай.";
        wcscat(str, L" ");
        wcscat(str, L"В добрый путь.");
        setlocale(LC_ALL, "en_US.utf8");
        printf("%ls", str);
    }

Output:

    Земля, прощай. В добрый путь.

### References

- C17 standard (ISO/IEC 9899:2018):

  - 7.29.4.3.1 The wcscat function (p: 315)

  - K.3.9.2.2.1 The wcscat_s function (p: 466)

- C11 standard (ISO/IEC 9899:2011):

  - 7.29.4.3.1 The wcscat function (p: 432)

  - K.3.9.2.2.1 The wcscat_s function (p: 642-643)

- C99 standard (ISO/IEC 9899:1999):

  - 7.24.4.3.1 The wcscat function (p: 378)

### See also

wcsncat wcsncat_s (C95)(C11) | appends a certain amount of wide characters from one wide string to another (function)
strcat strcat_s (C11) | concatenates two strings (function)
wcscpy wcscpy_s (C95)(C11) | copies one wide string to another (function)

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