Printing the gcc predefined macros to stdout

Any time you wanted to know the list of gcc used macros and their values. Here is the command details

touch foo.h; gcc -dM -E foo.h

will list all the macros used.

The option

-dM will generate the list of all #defines used by the pre-processor during execution, this also includes pre-defined macros.

-E will stop the compiler after pre-processing stage. Will not enter to the compiling stage. The output will be in the preprocessed form and will be sent to the stdout.