having the same function in multiple c source files

Question

I'm having a hard time finding out why i can't have the same function in several C source files. I always thought that i can't access functions in another source file as long as they ain't declared in a header file. Lets assume i have the following: main.c -> includes thread1.h & thread2.h thread1.h -> declares e.g. void * thread1(); thread1.c -> defines void * thread1(){} and defines void lock(){} thread2.h -> declares e.g. void * thread2(); thread2.c -> defines void * thread2(){} and defines void lock(){} Now gcc tells me i can't do that! gcc -pthread -Wall -o executable main.c thread1.c thread2.c ERROR: multiple definition of `lock' So my question now is: How can I accomplish what i want? I don't think that this is meant to be impossible. Otherwise all that C source code available within all the many C libraries would need to be unique. (nah would make no sense, or would it?) So i thought to myself about 3h ago that there must be a solution. That i must be missing something here. W…

Accepted Answer

You'll need that function `lock()` to be `static`.

```
static void lock() {..}
```

The reason is that functions with `static` are not visible outside of the "translation unit". In other (probably wrong) words, the static functions are private to the *.c file. Hence they dont cause linking errors in the linking stage, as you are currently having.

having the same function in multiple c source files

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