There are various ways to log information in the sac2c compiler.

There are kinds of ways to log information during compilation. src/libsac2c/support/debug.h and src/libsac2c/global/ctinfo.h

1. debug.h is for compiler debugging for the compiler developers.
2. The functions in ctinfo.h which are used to actually give feedback to the caller of the compiler.

debug.h

A modified version of the debug.h file by Fred Fish. Modify a lot by the sac team.

These macros are for compiler debugging for the compiler developers. Only present in a DEBUG build of the compiler.

This system allows you to print debug information to the console at different levels and for different tags.

You can get these debug messages for the entire compiler by using the -#d flag. If you want to only get messages for a certain compiler phase you can specify the debug prefix of the messages you want to see -#d,EX for a traversal with #define DBUG_PREFIX "EX". This is possible because the debug.h file allows you to only print messages with a certain prefix if you want.

You set the prefix by doing #define DBUG_PREFIX "TSM" at the top of the file you want to debug.

ctinfo functions

These functions actually provide feedback to the caller of the compiler. This messages are present in both debug builds and release builds of the compiler.

The logging follows different levels of verbosity. The caller sets the verbosity levels by using the -v flag. This info is from the top of the ctinfo.c file:

* Verbose level 0:
*
* Only error messages are printed.
*
* Verbose level 1:
*
* Error messages and warnings are printed.
*
* Verbose level 2:
*
* Error messages, warnings and basic compile time information, e.g. compiler
* phases,  are printed.
*
* Verbose level 3:
*
* Error messages, warnings and full compile time information are printed.
*
* Verbose level 4+:
*
* Additional compile time information is provided that typically is only
* of interest in certain situation.
*
* Default values are 1 for the product version and 3 for the developer version.

However ctinfo.c holds more logging functions like InternalCompilerErrorBreak which produces the OOOOOOOPS, your program crashed the compiler 8-(( message. Or for instance CTIerror which is used to print an error messages or CTIwarn to show warnings etc.