Beginning C programming- exceptions to whitespace irrelevant? include directive
 

New to programming. In several texts and online resources I have read that whitespace is irrelevant in C (except of course with strings).

Today I ran across the fact that my compiler choked on the following form of an include directive:

A space before or after the header filename produces a fatal compile error. I have never seen this mentioned (yet).

Any other exceptions to "whitespace irrelevant" you know of? I'm using Debian with current gcc.

Thanks,
Keith Ostertag

Hi there,

that's true, AFAIS.

This is -strictly speaking- not a C issue. The directives starting with a hash sign are parsed by the preprocessor, which used to be a separate tool in earlier compiler designs. Today, it's usually integrated in the compiler. Yet the preprocessing is a pass of its own, formally.

Anyway ... In your example, the < and > characters are considered string delimiters, and so the contents they enclose is a string. Note that you may use quotes instead of the < > and then you wouldn't have seen this as an exeption, would you?
However, there is a difference between using quotes and angle brackets with #include. If you use angle brackets, the compiler searches for the included file in its pre-configured include directories. If you use quotes, it searches in the source file's directory first, and then in the include directories.

[X] Doc CPU

Thank you for an informative response!

You might like the GNU C Preprocessor and the GNU C Reference Manual. For actual mastery you can get final draft standards free at www.open-std.org. Wrapping your head around the structure and detail of tho standards demands the kind of thinking that will serve you _very_ well professionally, but don't try them until you feel you have a real idea of what compilers and linkers and loaders do.