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15.1.2 Cannot Link Fortran Programs

On some systems, perhaps just those with out-of-date (shared?) libraries, unresolved-reference errors happen when linking g77-compiled programs (which should be done using g77).

If this happens to you, try appending -lc to the command you use to link the program, e.g. g77 foo.f -lc. g77 already specifies -lg2c -lm when it calls the linker, but it cannot also specify -lc because not all systems have a file named libc.a.

It is unclear at this point whether there are legitimately installed systems where -lg2c -lm is insufficient to resolve code produced by g77.

If your program doesn't link due to unresolved references to names like _main, make sure you're using the g77 command to do the link, since this command ensures that the necessary libraries are loaded by specifying -lg2c -lm when it invokes the gcc command to do the actual link. (Use the -v option to discover more about what actually happens when you use the g77 and gcc commands.)

Also, try specifying -lc as the last item on the g77 command line, in case that helps.