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C Preprocessor Output

The output from the C preprocessor looks much like the input, except that all preprocessor command lines have been replaced with blank lines and all comments with spaces. White-space characters within a line aren't altered; however, a space is inserted after the expansions of most macros. Also, pragmas are passed through verbatim.

Source file name and line number information is conveyed by lines of the form

# linenum file {digit}

which are inserted as needed into the middle of the input (but never within a string or character constant). Such a line means that the following line originated in file file at line linenum .

After the file name comes zero or more numeric flags: 1, 2 or 3, separated by spaces if multiple flags:

Flag
Description

1.

The start of a new file

2.

Return to a file (after having included another file).

3.

Text that follows comes from a system header file

(so certain warnings should be suppressed).


The GNU C Preprocessor

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