I have the following files:

```
//utils.hpp
namespace Utils {
  inline void saveFile(FileInfo &);
}

```

and implementation:

```
//utils.cpp
#include "./utils.hpp"
inline void Utils::saveFile(FileInfo & f) {}

```

and main.cpp

```
#include "./utils.hpp"
int main(){
  //...
  Utils::saveFile(f);
}

```

But when I try to compile, it gives me error:

```
main.cpp.o: In function `main':
main.cpp:(.text+0x358): undefined reference to `Utils::savePPMFile(FileInfo &)'
collect2: ld returned 1 exit status
make[2]: *** [simpletest] Error 1
make[1]: *** [CMakeFiles/simpletest.dir/all] Error 2
make: *** [all] Error 2

```

If I remove `inline`, everything works fine... How to use the inline function?