If a function takes as a parameter a string that is not changed by the function, the string parameter can be declared as a "const" string, or a PCSZ. PCSZ is defined in the header files as a "const" pointer to a NULL-delimited string.
The "const" means that the function will not change the contents of the string. The use of the "const" keyword is not specific to C++, many C compilers support it as well. However, the use of PCSZ allows for better optimization by the compiler and is more semantically compatible with C++.
The PCSZ data type is defined in addition to the PSZ data type. Existing code that calls functions that use PSZ will continue to work correctly, though they may cause warning or error messages when compiled.