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\n", str1, strlen(str1) );  

   // wstrlen gives the length of a wide character string
   wprintf(L"Length of '%s' : %d\n", wstr1, wcslen(wstr1) );  

   // A multibyte string: [A] [B] [C] [katakana A] [D] [\0]
   // in Code Page 932. For this example to work correctly,
   // the Japanese language support must be enabled by the
   // operating system.
   mbstr1 = "ABC" "\x83\x40" "D";  

   locale_string = setlocale(LC_CTYPE, "Japanese_Japan");  

   if (locale_string == NULL)
   {
      printf("Japanese locale not enabled. Exiting.\n");
      exit();
   }
   else
   {
      printf("Locale set to %s\n", 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\n", 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\n", mbstr1, _mbstrlen(mbstr1) );
   printf("Bytes in '%s' : %d\n", mbstr1, strlen(mbstr1) );     

}  

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