RTL functions are available in either ANSI/MBCS or Unicode definitions. For example, the RTL function strlen can be used in ANSI/MBCS mode as follows:

void StorePersonData(const char* name)
{
   PersistToDB(name, strlen(name));
}

A more portable way of writing this code is:

void StorePersonData(const _TCHAR* name)
{
   PersistToDB(name, _tcstrlen(name));
}

This example assumes that PersistToDB has a Unicode version. Note that for functions that are not going to change or float, you should use either char or wchar_t.

The following table is derived from the tchar.h header file. The char/ANSI column lists the floating functions that are appropriate when _TCHAR is mapped to char, the ANSI version of the function. The wchar_t/UNICODE column lists the functions for wchar_t, the UNICODE version of the function. The _TCHAR/Portable column lists the portable version of the function, which maps to the appropriate function (either the ANSI or UNICODE version) as determined by the current setting of the _TCHAR mapping option.  

Floating Function Definitions from tchar.h  

TCHAR Mapping 

Unicode in RAD Studio 

Enabling Unicode in Your Applications 

Enabling C++ Applications for Unicode