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 // f.for is a Fortran source file
 // c.c is a C source file   
 # gfortran -c f.for            // produce f.o
 # gcc -c c.c                   // produce c.o

since f.for calls some functions from c.c. How can I produce a third object file fc.o which will be used later to generate an executable with another C source code. explain: 

 # gcc/gfortran? (or other) -?? f.o c.o -o fc.o
 # gcc -o executable source.c fc.o

thank you

What I have done but not work: 

  # ar rvs fc.a f.o c.o  
  # gcc -o executable source.c fc.a

But it shows me error like : undefined reference to 'function_name_X'. function_name_X is in f.for

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  • ar rvs fc.a f.o c.o will get you a static library (fc.a), which you can use as if it were an object file made by merging f.o and c.o. Commented Oct 22, 2015 at 21:03
  • PSkocik: Yes, I'll try again this solution, perhaps it is the unique solution Commented Oct 22, 2015 at 21:08
  • Have you tried ld -r f.o c.o -o fc.o, then? (Dark Falcon's link) Commented Oct 22, 2015 at 21:08
  • You may be asking the wrong question. If you're producing all these object files in the same build process, then you don't need to make a combined object file. You can just link all the needed object files together to produce the final executable. Commented Oct 22, 2015 at 21:10
  • John Bollinger -> I have this this idea in my mind: if a.o depends on b.o, c.c depends on a.o , so # gcc -o exe c.c a.o b.o will work? Commented Oct 22, 2015 at 21:13

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Credit: PSkocik, John Bollinger
My comment :

I have this this idea in my mind: if a.o depends on b.o, c.c depends on a.o , so # gcc -o exe c.c a.o b.o will work?

should works. In fact, I listed all functions in f.o :

 # nm f.o

I find that Fortran add underscore '_' at the end of every function name, since I'm calling these functions from C without adding underscore at end, this error happened. According to this question: I added -fno-underscoring to gfortran compiler when generating f.o 

# gfortran -c f.for -fno-underscoring
# nm f.o

at this time, there is no underscore at the end.
Response to the question: 

# gcc -o executable source.c f.o c.o  // not need fc.o
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