std::mbstowcs

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

Null-terminated multibyte strings

Wide/multibyte conversions
mbsinit
mbtowc mbstowcs btowc mbrtowc mbsrtowcs mbrtoc8 (C++20) mbrtoc16 (C++11) mbrtoc32 (C++11) mblen	wctomb wcstombs wctob wcrtomb wcsrtombs c8rtomb (C++20) c16rtomb (C++11) c32rtomb (C++11) mbrlen
Types
mbstate_t

 

Defined in header <cstdlib>
std::size_t mbstowcs( wchar_t* dst, const char* src, std::size_t len);

Converts a multibyte character string from the array whose first element is pointed to by src to its wide character representation. Converted characters are stored in the successive elements of the array pointed to by dst. No more than len wide characters are written to the destination array.

Each character is converted as if by a call to std::mbtowc, except that the mbtowc conversion state is unaffected. The conversion stops if:

• The multibyte null character was converted and stored.
• An invalid (in the current C locale) multibyte character was encountered.
• The next wide character to be stored would exceed len.

Notes

In most implementations, this function updates a global static object of type std::mbstate_t as it processes through the string, and cannot be called simultaneously by two threads, std::mbsrtowcs should be used in such cases.

POSIX specifies a common extension: if dst is a null pointer, this function returns the number of wide characters that would be written to dst, if converted. Similar behavior is standard for std::mbsrtowcs.

Parameters

dst	-	pointer to wide character array where the wide string will be stored
src	-	pointer to the first element of a null-terminated multibyte string to convert
len	-	number of wide characters available in the array pointed to by dst

Return value

On success, returns the number of wide characters, excluding the terminating L'\0', written to the destination array.

On conversion error (if invalid multibyte character was encountered), returns static_cast<std::size_t> (-1).

Example

Run this code

#include <iostream>
#include <clocale>
#include <cstdlib>
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    std::wcout.imbue(std::locale("en_US.utf8"));
    const char* mbstr = u8"z\u00df\u6c34\U0001f34c"; // or u8"zß水🍌"
                        // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c";
    wchar_t wstr[5];
    std::mbstowcs(wstr, mbstr, 5);
    std::wcout << "wide string: " << wstr << '\n';
}

Output:

wide string: zß水🍌

See also

mbsrtowcs	converts a narrow multibyte character string to wide string, given state (function)
wcstombs	converts a wide string to narrow multibyte character string (function)
do_in [virtual]	converts a string from externT to internT, such as when reading from file (virtual protected member function of std::codecvt<InternT,ExternT,State>)