C - preprocessor printf with fixed string __FUNCTION__ and __VA_ARGS__

mr.simo · 03-15-2017, 07:02 PM

Hi all,

I am just courious with an implementation of preprocessor printf.

When possible I like to define a custom printf in order to always print the function name given by the __FUNCTION__ macro, plus the string I have to print:

Code:

#define myprintf (...) { printf("[ %s ]" , __FUNCTION__); printf(__VA_ARGS__); printf("\n"); }

Is there a way to do it without using 3 separate printf ?
I tried with this one but his one is not valid:

Code:

#define myprintf(fmt, ...) printf("[ %s ] " fmt, __FUNCTION__, __VA_ARGS__);

because I cannot use with a single string without parameters. For example, the following:

Code:

myprintf("Hello world");

would not be compiled.
Thanks.

ntubski · 03-15-2017, 07:55 PM

Does this help? https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html

rhamel · 03-15-2017, 08:05 PM

Code:

#include <stdio.h>

#define eprintf(fmt,...) fprintf(stderr, "[%s] %s", __FUNCTION__, fmt, ##__VA_ARGS__)

int main()
{
  eprintf("hello world");
}
test.cpp lines 1-8/8 (END)

Code:

gcc test.cpp -o mytest
./mytest
[main] hello world

This is with

Quote:

COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/i586-slackware-linux/5.3.0/lto-wrapper
Target: i586-slackware-linux
Configured with: ../gcc-5.3.0/configure --prefix=/usr --libdir=/usr/lib --mandir=/usr/man --infodir=/usr/info --enable-shared --enable-bootstrap --enable-languages=ada,c,c++,fortran,go,java,lto,objc --enable-threads=posix --enable-checking=release --enable-objc-gc --with-system-zlib --with-python-dir=/lib/python2.7/site-packages --enable-libstdcxx-dual-abi --with-default-libstdcxx-abi=gcc4-compatible --disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp --enable-lto --disable-install-libiberty --with-gnu-ld --verbose --enable-java-home --with-java-home=/usr/lib/jvm/jre --with-jvm-root-dir=/usr/lib/jvm --with-jvm-jar-dir=/usr/lib/jvm/jvm-exports --with-arch-directory=i386 --with-antlr-jar=/root/slackware-current/source/d/gcc/antlr-runtime-3.4.jar --enable-java-awt=gtk --disable-gtktest --with-arch=i586 --target=i586-slackware-linux --build=i586-slackware-linux --host=i586-slackware-linux
Thread model: posix
gcc version 5.3.0 (GCC)

rhamel · 03-15-2017, 08:06 PM

BTW, that's from https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html