tutorials/add-compiler-flag.md

+
+This tutorial teaches you how to add a new compiler flag called `-enable-foo` to the compiler.
+
+# Step 1
+
+First add a global variable where your flag will be stored into.
+This is done in `src/libsac2c/global/globals.mac`.
+
+Just add a macro like this:
+
+```c
+GLOBAL (bool, enable_foo, FALSE, xfree_dummy)
+//      ^-type  ^-name      ^-default   ^-free-function
+```
+
+Just look at what is already there. 
+For a string argument you need:
+
+```c
+GLOBAL (char *, enable_foo, NULL, xfree_char_ptr, )
+```
+
+# Step 2
+
+Then you have to add the flag to the `AnalyseCommandlineSac2c` function in `src/libsac2c/global/options.c`.
+This function is responsible for parsing the command line arguments and setting the global variables accordingly.
+
+Again just look at what is already there and extend this tutorial if you learned anything noteworthy.
+
+There two simple macros you can use: 
+
+- `ARGS_FLAG`
+- `ARGS_OPTION`
+
+There is also `ARGS_OPTION_BEGIN` and friends for one option that takes multiple flags like `-check pc`.
+Read `getoptions.h` for more information about these or look at the code for `-check`.
+
+## ARGS_FLAG
+
+With `ARGS_FLAG` the compiler option is just a boolean. 
+The macro takes a name and an expression. 
+The macro will run the expression if the option is passed.
+
+```c
+ARGS_FLAG ("enable-foo", global.enable_foo = TRUE);
+```
+
+## ARGS_OPTION
+
+This macro also takes a name and an expression.
+But with the expression of `ARGS_OPTION` you also can access the `ARG` variable.
+
+
+```c
+ARGS_OPTION ("enable-foo", global.enable_foo = STRcpy (ARG));
+```