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c++g++compiler-warningsclang++pragma

-Wundef is not being ignored with pragma in g++

Given the following code: 

#if MACRO_WITHOUT_A_VALUE
int var;
#endif

int main(){}

When compiled with, g++ -std=c++1z -Wundef -o main main.cpp,
it produces the following warning: 

main.cpp:1:5: warning: "MACRO_WITHOUT_A_VALUE" is not defined [-Wundef]
 #if MACRO_WITHOUT_A_VALUE
     ^

I'd like to keep the warning flag enabled, but suppress this particular instance.
I apply the following:

#ifdef __GNUC__
#pragma GCC diagnostic ignored "-Wundef"
#pragma GCC diagnostic push
#endif

#if MACRO_WITHOUT_A_VALUE
int var;
#endif

#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif

int main(){}

This only solves the problem in clang++.

The command clang++ -std=c++1z -Wundef -o main main.cpp builds without warnings.
The command g++ -std=c++1z -Wundef -o main main.cpp builds with the same [-Wundef] warning as before.

How can I suppress -Wundef warnings in g++? 

g++ (Ubuntu 5.1.0-0ubuntu11~14.04.1) 5.1.0
clang version 3.8.0
Solution

  • What I've done before when third party headers were inducing warnings was to wrap them in my own private header that uses #pragma GCC system_header to just silence all the warnings from that header. I use my own wrapper to keep the includes neat and allow for an additional customization point in the future if needed.