C library functions -mbstowcs()

C Standard Library - <stdlib.h>

Description

C Library FunctionsmbstowcsUsed to convert a multibyte string to a wide character string.

mbstowcsThe function is defined in the <stdlib.h> header file.

Declaration

Below is the declaration of the mbstowcs() function.

size_t mbstowcs(wchar_t *pwcs, const char *mbs, size_t n);

Parameter

  • pwcs: Points to a buffer used to store the converted wide character string. Ifpwcsis NULL, the function returns the required buffer length without performing the actual conversion.
  • mbs: Pointer to a multibyte string.
  • n: The maximum number of characters to convert. If, before encountering the terminating character, the conversion has already been performedncharacters, the conversion stops early.

Return Value

  • On success, returns the number of wide characters converted, excluding the terminating null character.
  • If an invalid multibyte sequence is encountered, returns(size_t)-1, and seterrno。

Example

The following example demonstrates the usage of the mbstowcs() function.

Example 1

#include <stdio.h> #include <stdlib.h> #include <string.h> int main() { int len; char *pmbnull = NULL; char *pmb = (char *)malloc( MB_CUR_MAX ); wchar_t *pwc = L"Hi"; wchar_t *pwcs = (wchar_t *)malloc( sizeof( wchar_t )); printf("Convert to a multibyte string\n"); len = wcstombs( pmb, pwc, MB_CUR_MAX); printf("Converted character %d\n", len); printf("Hexadecimal value of the first multibyte character: %#.4x\n", pmb); printf("Convert back to a wide character string\n"); len = mbstowcs( pwcs, pmb, MB_CUR_MAX); printf("Converted character %d\n", len); printf("Hexadecimal value of first wide character: %#.4x\n\n", pwcs); return(0); }

Let us compile and run the above program, which will produce the following result:

转换为多字节字符串
被转换的字符 1
第一个多字节字符的十六进制值：0x19a60010
转换回宽字符字符串
被转换的字符 1
第一个宽字符的十六进制值：0x19a60030

Example 2

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

int main() {
    // Set the current locale to the locale specified by the user environment variable
    setlocale(LC_ALL, "");

    // Define a multibyte string
    const char *mbstr = "Hello, world!";
    // Calculate the required buffer size
    size_t wcs_len = mbstowcs(NULL, mbstr, 0) + 1;

    // Allocate wide character buffer
    wchar_t *wcs = (wchar_t *)malloc(wcs_len * sizeof(wchar_t));
    if (wcs == NULL) {
        perror("malloc");
        return 1;
    }

    // Perform conversion
    mbstowcs(wcs, mbstr, wcs_len);

    // Print wide character string
    wprintf(L"%ls\n", wcs);

    // release memory
    free(wcs);

    return 0;
}

Let us compile and run the above program, which will produce the following result:

Hello, 世界!

Notes

  1. Locale: The behavior of the function is affected by the currentlocalesetting, usually when callingmbstowcsNeed to call beforesetlocaleto set the appropriatelocale。
  2. Error Handling: If the input multibyte string contains an invalid multibyte sequence, the function returns(size_t)-1and seterrno. The caller needs to check the return value and handle possible errors.
  3. Memory allocation: The caller needs to ensurepwcsThere is enough space to store the converted wide character string. This can be done by first callingmbstowcs, thenpwcsSet toNULLto calculate the required buffer size.

C Standard Library - <stdlib.h>

other extensions