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?
views:
108answers:
5
A:
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.
Alexander Rafferty
2010-09-30 00:21:31
This won't print at compile-time, which is what I'm thinking OP is looking for.
Bob Kaufman
2010-09-30 00:23:31
I assumed he meant printing at run-time.
Alexander Rafferty
2010-09-30 00:30:52
I was asking about compile-time. Thanks!
Drew Wagner
2010-10-01 13:59:23
+6
A:
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!" )
You
2010-09-30 00:24:13
Which begs the question, can you put a directive based on a compilation flag to swap "pragma message" and "warning" somehow? For example, something like: `#ifdef _LINUX #define #preprocmsg "#warning" else #define #preprocmsg "#pragma message"`... I'll have to try that but instinct tells me the answer is no.
Bryan
2010-09-30 00:41:30
@Bryan: The best you can do is put `#ifdef _MSC_VER` `#pragma MESSAGE` `#else` `#warning MESSAGE` `#endif` into `warning.h`, then do the two-line `#define MESSAGE "message here"` `#include "warning.h"` when you want to output a message.
caf
2010-09-30 01:58:39
+3
A:
The following are supported by MSVC, and GCC.
#pragma message("stuff")
#pragma message "stuff"
Clang has begun adding support recently, see here for more.
Matt Joiner
2010-09-30 00:26:19
+1
A:
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.
nos
2010-09-30 00:28:37