Is it possible to let gnu cpp preserve include macro?

Question

I'm using gnu cpp for some tests and hope it preserves the #include macro and extends other user-defined macro meanwhile. Is it possible? Here's a piece of code(foo.c):

#include <stdio.h>
#define NEWLINE(str) str "\n"
int main(){
  puts(NEWLINE("foo"));
}

And I hope the result of cpp foo.c to be:

#include <stdio.h>
int main(){
  puts("foo\n");
}

And why exactly do you ask? You could copy-paste the preprocessed output after some given point (e.g. after the last #include), but even that is not very sensible: you want to read MAP_FAILED not ((void *) -1) in your source code.... — Basile Starynkevitch
– Basile Starynkevitch, Commented Dec 18, 2012 at 19:43

Clement J. · Accepted Answer · 2012-12-18 08:51:51Z

1

You could use a script to comment out every #include, run cpp and then remove these comments.

answered Dec 18, 2012 at 8:51

Clement J.

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2 Comments

Basile Starynkevitch Over a year ago

It might not behave as wanted. Imagine some first included header #define-ing something which a secondly included header would test with #ifdef (and this is a common case, often hidden)

Clement J. Over a year ago

You're right but if I understand correctly what @Hongxu Chen want #define in a header don't have to apply outside of this file.

Some programmer dude · Accepted Answer · 2012-12-18 08:21:10Z

0

If I understand you correctly, you want to use the preprocessor to preprocess only certain parts but not others. This is generally not possible. The only way to do this is to add conditions to the source, i.e. use e.g. #ifdef and #endif around the parts you want expanded, and pass a define on the command line to the preprocessor.

answered Dec 18, 2012 at 8:21

Some programmer dude

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3 Comments

Hongxu Chen Over a year ago

So I have to let cpp gnu ignore those #define macros first and preprocess for others?

Some programmer dude Over a year ago

@HongxuChen No, you have to use conditional compilation techniques to tell the preprocessor which part it should preprocess and which part it should not.

Hongxu Chen Over a year ago

Got it! I know what I can do now, although the requirement is a bit different:-)

Basile Starynkevitch · Accepted Answer · 2012-12-18 08:18:22Z

0

No, it is not possible. However, the line information is usually available in lines starting with # in the preprocessor output.

You could use perhaps some other preprocessor like e.g. gpp

answered Dec 18, 2012 at 8:18

Basile Starynkevitch

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