Edit

Share via

Using Functions That Have No Unicode Equivalents

  • Article

Functions that have not been implemented with a Unicode version have typically been replaced by more powerful or extended functions that do support Unicode. For example, if you are porting code that calls the OpenFile function, your application can support Unicode by using the CreateFile function instead.

If a function has no Unicode equivalent, the application can map characters to and from 8-bit character sets before and after the function call. For example, the number-formatting functions atoi and itoa use only the digits 0 through 9. Normally, mapping Unicode to 8-bit characters causes loss of data, but this can be avoided by making the code type-independent and making the expressions conditional. The statements in the following example, written for 8-bit characters, are type-dependent and should be changed to support Unicode.

char str[4] = "137";

int num = atoi(str);

These statements can be rewritten as follows to make them type-independent.

TCHAR tstr[4] = TEXT("137");

#ifdef UNICODE
size_t cCharsConverted;
CHAR strTmp[SIZE]; // SIZE equals (2*(sizeof(tstr)+1)). This ensures enough
                   // room for the multibyte characters if they are two 
                   // bytes long and a terminating null character. See Security 
                   // Alert below. 

wcstombs_s(&cCharsConverted, strTmp, sizeof(strTmp), (const wchar_t *)tstr, sizeof(strTmp));
num = atoi(strTmp);

#else

int num = atoi(tstr);

#endif

In this example, the standard C library function wcstombs translates Unicode to ASCII. The example relies on the fact that the digits 0 through 9 can always be translated from Unicode to ASCII, even if some of the surrounding text cannot. The atoi function stops at any character that is not a digit.

Your application can use the National Language Support (NLS) LCMapString function to process text that includes the native digits provided for some of the scripts in Unicode.

Caution

Using the wcstombs function incorrectly can compromise the security of your application. Make sure that the application buffer for the string of 8-bit characters is at least of size 2*(char_length +1), where char_length represents the length of the Unicode string. This restriction is made because, with double-byte character sets (DBCSs), each Unicode character can be mapped to two consecutive 8-bit characters. If the buffer does not hold the entire string, the result string is not null-terminated, posing a security risk. For more information about application security, see Security Considerations: International Features.

 

Using Unicode and Character Sets