All the functions in your local C function library are available while you are programming in C++. You should look hard at the function library before defining your own function – there’s a good chance that someone has already solved your problem for you, and probably given it a lot more thought and debugging.

A word of caution, though: many compilers include a lot of extra functions that make life even easier and are tempting to use, but are not part of the Standard C library. If you are certain you will never want to move the application to another platform (and who is certain of that?), go ahead –use those functions and make your life easier. If you want your application to be portable, you should restrict yourself to Standard library functions. If you must perform platform-specific activities, try to isolate that code in one spot so it can be changed easily when porting to another platform. In C++, platform-specific activities are often encapsulated in a class, which is the ideal solution.

The formula for using a library function is as follows: first, find the function in your programming reference (many programming references will index the function by category as well as alphabetically). The description of the function should include a section that demonstrates the syntax of the code. The top of this section usually has at least one #include line, showing you the header file containing the function prototype. Duplicate this #include line in your file so the function is properly declared. Now you can call the function in the same way it appears in the syntax section. If you make a mistake, the compiler will discover it by comparing your function call to the function prototype in the header and tell you about your error. The linker searches the Standard library by default, so that’s all you need to do: include the header file and call the function.