CPP has a small number of internal limits. This section lists the limits which the C standard requires to be no lower than some minimum, and all the others we are aware of. We intend there to be as few limits as possible. If you encounter an undocumented or inconvenient limit, please report that to us as a bug. (See the section on reporting bugs in the GCC manual.)
Where we say something is limited only by available memory, that
means that internal data structures impose no intrinsic limit, and space
is allocated with
malloc or equivalent. The actual limit will
therefore depend on many things, such as the size of other things
allocated by the compiler at the same time, the amount of memory
consumed by other processes on the same computer, etc.
We impose an arbitrary limit of 200 levels, to avoid runaway recursion. The standard requires at least 15 levels.
The C standard mandates this be at least 63. CPP is limited only by available memory.
The C standard requires this to be at least 63. In preprocessor conditional expressions, it is limited only by available memory.
The preprocessor treats all characters as significant. The C standard requires only that the first 63 be significant.
The standard requires at least 4095 be possible. CPP is limited only by available memory.
USHRT_MAX, which is no smaller than 65,535. The minimum
required by the standard is 127.
The C standard requires a minimum of 4096 be permitted. CPP places no limits on this, but you may get incorrect column numbers reported in diagnostics for lines longer than 65,535 characters.
The standard does not specify any lower limit on the maximum size of a source file. GNU cpp maps files into memory, so it is limited by the available address space. This is generally at least two gigabytes. Depending on the operating system, the size of physical memory may or may not be a limitation.