Using gcc with multiple files - c

Question

I am trying to generate an executable file test from a c file test.c.
test.c includes the main() function, but I also want to include functions from stuff.c. I was told to declare functions in stuff.h and then run the command gcc -Wall -std=c99 stuff.c stuff.h test.c -o test.
I know what each component of this does, but this is the first time I've tried to use gcc with multiple input files. When I try to run this command, it fails, and I get the error clang: error: cannot specify -o when generating multiple output files.
As far as I'm aware, I'm only trying to generate one output file, so I assume this command is set up incorrectly. How can I fix it?

Answer 1

Here are your errors
you are not suppose to compile .h files in c so try this:
gcc -Wall -std=c99 stuff.c test.c -o test
gcc depends also on environment that you run it on. On my system if I do gcc -Wall -std=c99 stuff.c stuff.h test.c -o test it will work, because compiler is set that way. On some machines it might be different. So if for some strange reason #1 does not work you have to do following:
gcc -Wall -std=c99 -c stuff.c test.c
gcc -Wall -std=c99 stuff.o test.o -o test
./test
But your error clang: error: cannot specify -o when generating multiple output files is due to some code error, perhaps header file problems. So post your code

Answer 2

The difference seems to be due to a difference of behavior between gcc and clang as shown in the following example.
~/test $ ls -ltr
total 4
-rw-rw-r-- 1 arusaha arusaha 0 Apr 3 13:19 b.h
-rw-rw-r-- 1 arusaha arusaha 0 Apr 3 13:19 b.c
-rw-rw-r-- 1 arusaha arusaha 14 Apr 3 13:20 a.c
~/test $ clang -Wall -std=c99 b.c b.h a.c -o ab
clang: error: cannot specify -o when generating multiple output files
~/test $ gcc -Wall -std=c99 b.c b.h a.c -o ab
~/test $ ls -ltr
total 16
-rw-rw-r-- 1 arusaha arusaha 0 Apr 3 13:19 b.h
-rw-rw-r-- 1 arusaha arusaha 0 Apr 3 13:19 b.c
-rw-rw-r-- 1 arusaha arusaha 14 Apr 3 13:20 a.c
-rwxrwxr-x 1 arusaha arusaha 8576 Apr 3 13:21 ab
~/test $
Compiling multiple files is supported in gcc, see http://www.network-theory.co.uk/docs/gccintro/gccintro_11.html
I was curious how gcc command can throw a clang error and that turned out to be a clue :). It is possible that OP's gcc is pointing to clang (and that can be confusing).
From gcc manpage at http://man7.org/linux/man-pages/man1/gcc.1.html
-o file
Place output in file file. This applies to whatever sort of
output is being produced, whether it be an executable file, an
object file, an assembler file or preprocessed C code.
If -o is not specified, the default is to put an executable file
in a.out, the object file for source.suffix in source.o, its
assembler file in source.s, a precompiled header file in
source.suffix.gch, and all preprocessed C source on standard
output.
From clang manpage at https://clang.llvm.org/docs/CommandGuide/clang.html
-o <file> Write output to file.
To me, the difference of behavior is not exactly clear by just reading the man page but I could be wrong.