Q: Why is my C/C++/FORTRAN program no longer working when I didn't change anything since it last worked (a while ago)?
Note that programs compiled under SunOS 5.7 will not run under SunOS 5.6, so check the OS version on the systems you are using (with the command 'uname -r'). Also, use of GCC under SunOS 5.7 is unsupported until at least version 3.1 (type 'gcc -v' to check the current version), although an experimental version is availably by putting /s/dynamo/help/bin first in your $PATH (e-mail for details).
Otherwise, your problem is probably due to the fact that the compilers and/or related libraries were patched or upgraded in the interval. Check the ``last change'' information for Sun compilers or the GCC (scroll down for the latter). For the Sun compilers, you could also look under the very technical ``special install instructions'' of the README.* files found in each of the directories under /s/server/root/patches/6.2/old/normal/ (not all of which are relevant).
If there was a change, you should recompile your program. If it uses third-party libraries (e.g., PGPLOT), see the notes at the bottom of the software web page for additional help.
If this does not solve your problem, it is possible that there were some significant changes in the language itself that affect your particular program. Check the documentation for Sun compilers or GCC. (This seems to affect C++ the most.)
Except in rare circumstances (system installation debugging), we will not be able to debug your program, much less rewrite it for you, so you will have to get help from the sources referenced in the compilers' online documentation. (You may want to first use the other compiler--you were not using--to check whether your problem is compiler-dependent...)