DOUG BELL

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8 years, 3 months ago.

how to define a function in another .c file?

I have main.c and test.c and I can't access a function in test.c by main.c

I get this error: Error: Undefined symbol blah() (referred from main.NUCLEO_F091RC.o).

main.c has: ... extern void blah( void );

void blahblah( void ) { blah(); }

test.c has:

void blah( void ) { int a=5; int b=5*5; }

Both files are within the project folder, and not within any subfolder.

1 Answer

Zoltan Hudak
8 years, 3 months ago.

Hello Dough,
I have tested your code and it compiles smoothly with no errors. Please check the file names in your project because when I rename main.c to main.cpp then I get the same error as you have reported. It's because C++ is using name mangling. The solution is

  • tell the compiler that blah() is not a C++ but C function as follows:

main.cpp

extern "C" void blah(void);

int main() {
     blah(); 
}


  • or rename also test.c to test.cpp and then blah() will be compiled as a C++ function.

Accepted Answer