C++ mbrtowc()

Introduction

The C++ library function mbrtowc() is used to convert a multibyte character to a wide character. It is part of the <cuchar> header and is a commonly used function in internationalization (i18n) and localization (l10n) tasks, where character encodings play a crucial role.

Function Signature

The function has the following signature:

#include <cuchar>
size_t mbrtowc(wchar_t* pwc, const char* s, size_t n, mbstate_t* ps);

Parameters

• pwc (output parameter) - Pointer to a wide character where the result is stored.
• s (input parameter) - Pointer to the multibyte character.
• n (input parameter) - The number of bytes to inspect in the multibyte character 's'.
• ps (input/output parameter) - Pointer to the conversion state object of type 'mbstate_t'.

Return Value

The function returns the number of bytes consumed from the multibyte character sequence 's' and converted into a wide character. The following values are possible:

• 0: If the multibyte character sequence is the null string.
• -1: If the multibyte character is an invalid character or incomplete character.
• n: If the multibyte character is invalid for the current encoding, but is completed.

Conversion State

The mbrtowc() function uses a conversion state object, mbstate_t, to keep track of the state between successive calls. The object is initialized to an initial conversion state by mbsinit() or memset() before making the first call to mbrtowc().

Example

The following example demonstrates the use of mbrtowc() function:

#include <iostream>
#include <cuchar>

int main() {
    const char* mbstr = u8"Bücher"; // German word for "books"
    wchar_t wc;
    mbstate_t state = {};

    size_t result = mbrtowc(&wc, mbstr, std::strlen(mbstr), &state);
    if (result == static_cast<size_t>(-1)) {
        std::cout << "Invalid multibyte character or incomplete character encountered";
    }
    else if (result == static_cast<size_t>(-2)) {
        std::cout << "Invalid multibyte character for the current encoding";
    }
    else if (result > 0) {
        std::wcout << "Converted wide character: " << wc;
    }
    
    return 0;
}

The expected output of this program would be:

Converted wide character: Bü

Conclusion

The mbrtowc() function is a powerful tool in C++ for converting multibyte characters to wide characters. With proper understanding and correct usage, it enables developers to work with different character encodings efficiently, ensuring proper internationalization and localization support in their software.