strlen, wcslen, _mbslen, _mbslen_l, _mbstrlen, _mbstrlen_l, setlocale(LC_CTYPE, "Japanese_Japan")（MSDN的官方示例）

// crt_strlen.c  
// Determine the length of a string. For the multi-byte character  
// example to work correctly, the Japanese language support for  
// non-Unicode programs must be enabled by the operating system.  
  
#include <string.h>  
#include <locale.h>  
  
int main()  
{  
   char* str1 = "Count.";  
   wchar_t* wstr1 = L"Count.";  
   char * mbstr1;  
   char * locale_string;  
  
   // strlen gives the length of single-byte character string  
   printf("Length of '%s' : %d
", str1, strlen(str1) );  
  
   // wstrlen gives the length of a wide character string  
   wprintf(L"Length of '%s' : %d
", wstr1, wcslen(wstr1) );  
  
   // A multibyte string: [A] [B] [C] [katakana A] [D] []  
   // in Code Page 932. For this example to work correctly,  
   // the Japanese language support must be enabled by the  
   // operating system.  
   mbstr1 = "ABC" "x83x40" "D";  
  
   locale_string = setlocale(LC_CTYPE, "Japanese_Japan");  
  
   if (locale_string == NULL)  
   {  
      printf("Japanese locale not enabled. Exiting.
");  
      exit(1);  
   }  
   else  
   {  
      printf("Locale set to %s
", locale_string);  
   }  
  
   // _mbslen will recognize the Japanese multibyte character if the  
   // current locale used by the operating system is Japanese  
   printf("Length of '%s' : %d
", mbstr1, _mbslen(mbstr1) );  
  
   // _mbstrlen will recognize the Japanese multibyte character  
   // since the CRT locale is set to Japanese even if the OS locale  
   // isnot.   
   printf("Length of '%s' : %d
", mbstr1, _mbstrlen(mbstr1) );  
   printf("Bytes in '%s' : %d
", mbstr1, strlen(mbstr1) );     
  
}  

https://msdn.microsoft.com/en-us/library/78zh94ax.aspx