XL C/C++ generates a default configuration file /etc/opt/ibmcmp/vac/8.0/vac.cfg at installation time (see the XL C/C++ Installation Guide for more information on the various tools you can use to generate the configuration file during installation). The configuration file specifies information that the compiler uses when you invoke it.
If you are running on a single-user system, or if you already have a compilation environment with compilation scripts or makefiles, you may want to leave the default configuration file as it is. Otherwise, especially if you want many users to be able to choose among several sets of compiler options, you may want to modify existing stanzas or add new named stanzas to the configuration file. For example, to make -qnoro the default for the xlc compiler invocation command, add -qnoro to the xlc stanza in your copied version of the configuration file.
You can create new commands that are links to the existing commands. For example, to create a link to the xlc_r command, you could specify something similar to the following:
ln -s /opt/ibmcmp/vacpp/8.0/bin/xlc_r /home/lisa/bin/my_xlc
You can link the compiler invocation command to several different names. The name you specify when you invoke the compiler determines which stanza of the configuration file the compiler uses. You can add other stanzas to your copy of the configuration file to customize your own compilation environment. You can use the -F option with the compiler invocation command to make links to select additional stanzas or to specify a specific stanza in another configuration file. For example:
xlc myfile.c -Fmyconfig.cfg:SPECIAL
would compile myfile.c using the SPECIAL stanza in a myconfig.cfg configuration file that you had created.
When you run the compiler under another name, it uses the options, libraries, and so on, that are listed in the corresponding stanza.