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I'm performing some source processing between C preprocessing and C compilation. At the moment I:

  1. gcc -E file.c > preprocessed_file.c.
  2. Do more stuff to preprocessed_file.c.
  3. Continue the compilation with preprocessed_file.c.

If you attempt to compile preprocessed_file.c as you would if it was normal C (step 3) you get lots of the following:

/usr/include/stdio.h:257: error: redefinition of parameter ‘restrict’ /usr/include/stdio.h:257: error: previous definition of ‘restrict’ was here /usr/include/stdio.h:258: error: conflicting types for ‘restrict’ /usr/include/stdio.h:258: error: previous definition of ‘restrict’ was here /usr/include/stdio.h:260: error: conflicting types for ‘restrict’ [...]

And that's just using #include <stdio.h> in file.c. Fortunately there's an option to tell GCC it's acting on C code that has already been preprocessed by specifying the language that is being compiled as c-cpp-output (see -x on this page). But it doesn't work. I just get this:

$ gcc -x c-cpp-output -std=c99 bar.c i686-apple-darwin9-gcc-4.0.1: language c-cpp-output not recognized i686-apple-darwin9-gcc-4.0.1: language c-cpp-output not recognized ld warning: in bar.c, file is not of required architecture Undefined symbols: "_main", referenced from: start in crt1.10.5.o ld: symbol(s) not found collect2: ld returned 1 exit status

And exactly the same response with a newer version of GCC:

$ gcc-mp-4.4 -x c-cpp-output -std=c99 bar.c [same error stuff comes here]
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3 Answers 3

Reset to default
4

Looks like a typo in the GCC docs - try '-x cpp-output' instead.

gcc -E helloworld.c > cppout gcc -x cpp-output cppout -o hw ./hw Hello, world!
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3 Comments

Well that worked with a hello world but not with my code. Lemme see what's going on.
Maybe try 'gcc -x cpp-output -std=c99 xyz.cppoutput'?
is there a similar option in visual studio ?
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The warnings about restrict are due to the fact that it is a keyword in C99. So, you have to pre-process and compile your code using the same standard.

The error about _main is because your file doesn't define main()? Doing the following should work:

gcc -c -std=c99 bar.c

and it will create bar.o. If your bar.c has a main() defined in it, maybe it is not called bar.c? For example, I created a bar.c with a valid main(), and did:

gcc -E -std=c99 bar.c >bar.E gcc -std=c99 bar.E

and got:

Undefined symbols: "_main", referenced from: start in crt1.10.6.o ld: symbol(s) not found collect2: ld returned 1 exit status

In that case, you need the -x c option:

gcc -x c -std=c99 bar.E

(Or, as Nikolai mentioned, you need to save the pre-processed file to bar.i.)

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2

Save the file with the .i suffix after pre-processing. Gcc man page:

 file.i C source code which should not be preprocessed. file.ii C++ source code which should not be preprocessed.
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$ gcc -std=c99 bar.i In file included from bar.h:4, from bar.cex:4: /usr/include/stdio.h:327: error: syntax error before ‘--’ token /usr/include/stdio.h:335: error: syntax error before ‘__stdoutp’ /usr/include/stdio.h:383: error: static declaration of ‘__sputc’ follows non-static declaration /usr/include/stdio.h:334: error: previous declaration of ‘__sputc’ was here
@Ollie: How are you pre-processing the files? What's the command you use for that?

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