Duplicate Symbol in C

Question

I have two source files:

Source FIle 1 (assembler.c):

#include "parser.c"
int main() {
    parse_file("test.txt");
    return 0;
}

Source File 2 (parser.c):

void parse_file(char *config_file);
void parse_file(char *src_file) {
    // Function here
}

For some reason, when compiling it is giving me the following error: duplicate symbol _parse_file in ./parser.o and ./assembler.o for architecture x86_64

Why is it giving me a duplicate symbol for parse_file? I am just calling the function here... No?

Answer 1

First off, including source files is a bad practice in C programming. Normally, the current translation unit should consist of one source file and a number of included header files.

What happens in your case is that you have two copies of the parse_file function, one in each translation unit. When parser.c is compiled to an object file, it has its own parse_file function, and assembler.c also has its own.

It is the linker that complains (not the compiler) when given two object files as an input, each of which contains its own definition of parse_file.

You should restructure your project like this:

parser.h

void parse_file(char *);

parser.c

void parse_file(char *src_file) {
    // Function here
}

assembler.c

/* note that the header file is included here */
#include "parser.h"

int main (void) {
    parse_file("test.txt");
    return 0;
}