GPC is a command-line compiler, i.e., to compile a program you have to invoke gpc passing it the name of the file you want to compile, plus options.
GPC supports all command-line options that GCC knows, except for many preprocessor options. For a complete reference and descriptions of all options, see GCC Command Options (the GCC Manual). Below, you will find a list of the additional options that GPC supports, and a list of GPC's most important options (including some of those supported by GCC as well).
You can mix options and file names on the command line. For the most part, the order doesn't matter. Order does matter, e.g., when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Note: Since many options have multiletter names; multiple single-letter options may not be grouped as is possible with many other programs: -dr is very different from -d -r.
Many options have long names starting with -- or, completely equivalent -f. E.g., --mixed-comments is the same as -fmixed-comments. Some options tell GPC when to give warnings, i.e. diagnostic messages that report constructs which are not inherently erroneous but which are risky or suggest there may have been an error. Those options start with -W.
Most GPC specific options can also be changed during one compilation by using compiler directives in the source, e.g. {$X+} or {$extended-syntax} for --extended-syntax (see Compiler Directives).
GPC understands the same environment variables GCC does (see Environment Variables Affecting GCC (the GCC manual)). In addition, GPC recognizes GPC_EXEC_PREFIX with the same meaning that GCC_EXEC_PREFIX has to GCC. GPC also recognizes GCC_EXEC_PREFIX, but GPC_EXEC_PREFIX takes precedence.
Some of the long options (e.g., --unit-path) take an argument. This argument is separated with a = sign, e.g.:
--unit-path=/home/foo/units