Troubleshooting in the GCC C++ compiler

GCC provides several help and diagnostic options to assist in troubleshooting problems with the compilation process. The options that you can use to ease your troubleshooting process are explained in the upcoming sections.

Help for command-line options

Use the help options to get a summary of the top-level GCC command-line options. The command for this is as follows:

g++ --help

To display a complete list of the options for GCC and its associated programs, such as the GNU Linker and GNU Assembler, use the preceding help option with the verbose (-v) option:

g++ -v --help

The complete list of options produced by the preceding command is extremely long—you may wish to go through it using the more command or redirect the output to a file for reference, as follows:

g++ -v --help 2>&1 | more

Version numbers

You can find the version number of your installed GCC installation using the version option, as shown in the following command:

g++ --version

In my system, if I run the preceding command, I will get an output like this:

g++ (x86_64-posix-seh-rev2, Built by MinGW-W64 project) 4.9.2

This depends on your setting that you adjust at the installation process.

The version number is important when investigating compilation problems, since older versions of GCC may be missing some features that a program uses. The version number has the major-version.minor-version or major-version.minor-version.micro-version form, where the additional third "micro" version number (as shown in the preceding command) is used for subsequent bug fix releases in a release series.

The verbose compilation

The -v option can also be used to display detailed information about the exact sequence of commands that are used to compile and link a program. Here is an example that shows you the verbose compilation of the hello.cpp program:

g++ -v -Wall rangen.cpp

After this, you will get something like this in the console:

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=C:/mingw-w64/bin/../libexec/gcc/x86_64-w64-mingw32/4.9.2/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../../../src/gcc-4.9.2/configure –
...Thread model: posix
gcc version 4.9.2 (x86_64-posix-seh-rev2, Built by MinGW-W64 project)
...

The output produced by the -v option can be useful whenever there is a problem with the compilation process itself. It displays the full directory paths used to search for header files and libraries, the predefined preprocessor symbols, and the object files and libraries used for linking.