C Linking Error: undefined reference to 'main'

Question

I have read the other answers on this topic, and unfortunately they have not helped me. I am attempting to link several c programs together, and I am getting an error in response:

$ gcc -o runexp.o scd.o data_proc.o -lm -fopenmp /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crt1.o: In function `_start': (.text+0x20): undefined reference to `main' collect2: ld returned 1 exit status make: * [runexp] Error 1 

I have exactly one main function and it is in runexp. The form is

int main(void) {     ...;      return 0; } 

Any thoughts on why I might get this error? Thanks!

Answer 1

You should provide output file name after -o option. In your case runexp.o is treated as output file name, not input object file and thus your main function is undefined.

Answer 2

You're not including the C file that contains main() when compiling, so the linker isn't seeing it.

You need to add it:

$ gcc -o runexp runexp.c scd.o data_proc.o -lm -fopenmp