Is there a portable way to print a message from the C preprocessor?

PrintingC Preprocessor

Printing Problem Overview

I would like to be able to do something like

#print "C Preprocessor got here!"

for debugging purposes. What's the best / most portable way to do this?

Printing Solutions

Solution 1 - Printing

The warning directive is probably the closest you'll get, but it's not entirely platform-independent:

#warning "C Preprocessor got here!"

AFAIK this works on most compilers except MSVC, on which you'll have to use a pragma directive:

#pragma message ( "C Preprocessor got here!" )

Solution 2 - Printing

The following are supported by MSVC, and GCC.

#pragma message("stuff")
#pragma message "stuff"

Clang has begun adding support recently, see here for more.

Solution 3 - Printing

You might want to try: #pragma message("Hello World!")

Solution 4 - Printing

Most C compilers will recognize a #warning directive, so

 #warning "Got here"

There's also the standard '#error' directive,

 #error "Got here"

While all compilers support that, it'll also stop the compilation/preprocessing.

Solution 5 - Printing

#pragma message("foo")

works great. Also wouldn't stop compilation even if you use -Werror

Solution 6 - Printing

Another solution is to use comments plus a shell script to process them. This takes some discipline (or a shell script which catches typos).

For example, I add comments formatted //TODO and then a shell script which collects all of them into a report.

For more complex use cases, you can try to write your own simple preprocessor. For example, you could edit your sources as *.c2 files. The simple preprocessor would read the source, look for //TODO, and write printf("TODO ...") into the output *.c file.

Solution 7 - Printing

You can't. Preprocessors are processed before the C code. There are no preprocessor directives to print to the screen, because preprocessor code isn't executed, it is used to generate the C code which will be compiled into executable code.

Anything wrong with:

#ifdef ...
printf("Hello");
#endif

Because this is all you can do as far as preprocessors go.

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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionAndrew WagnerView Question on Stackoverflow
Solution 1 - PrintingYouView Answer on Stackoverflow
Solution 2 - PrintingMatt JoinerView Answer on Stackoverflow
Solution 3 - PrintingRuelView Answer on Stackoverflow
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Solution 5 - PrintingMartinView Answer on Stackoverflow
Solution 6 - PrintingAaron DigullaView Answer on Stackoverflow
Solution 7 - PrintingAlexander RaffertyView Answer on Stackoverflow