How come Im not seeing an improvement in compile time even though Ive started using the precompiled header facility of the C++ compiler?
Using precompiled headers does not guarantee faster compile times. Precompiled headers impose some overhead that is not present when you compile files directly. To gain a performance advantage, the precompiled headers must have some redundancy that precompilation can eliminate. For example, a program that is highly likely to benefit from precompilation is one that includes many system headers, iostreams, STL headers, and project headers. Those files contain conditionally-compiled code. Some headers are included multiple times, and the compiler must scan over the entire file if only to discover there is nothing to do in the redundant includes. System headers typically have hundreds of macros to expand. Using a precompiled header means opening one file instead of dozens. The multiple includes that do nothing are eliminated, as are comments and extra white space. The macros in the headers are pre-expanded. Typically, these savings add up to a significant reduction in compile time.
