Compilation with multiple PreCompiled Header (PCH) files

More than one PCH file might apply to a given compilation. If so, the largest is used, that is, the one representing the most preprocessing directives from the primary source file. For example, a primary source file might begin with:

#include "xxx.h"
#include "yyy.h"
#include "zzz.h"

If there is one PCH file for xxx.h and a second for xxx.h and yyy.h, the latter PCH file is selected, assuming that both apply to the current compilation. Additionally, after the PCH file for the first two headers is read in and the third is compiled, a new PCH file for all three headers is created if the requirements for PCH file creation are met.