Question

I have a header file called custom_types.h that was working fine until now. I have a few enums declared in it and there is no implementation file with the same name.

These are the two declarations in the file:

enum playback_type {
    NOTE_PB,
    SONG_PB
};

enum note_name {
    C_REG = 1,
    C_SHARP = 2,
    D_REG = 3
};

Now for some reason I’m getting conflicting declaration errors (full size here):

You guys have any idea why this is happening? I don’t understand how a single definition can be conflicting.

Answer 1

Use guards:

//custom_types.h

#ifndef custom_types_h  //this is called guard!
#define custom_types_h   

enum playback_type {
    NOTE_PB,
    SONG_PB
};

enum note_name {
    C_REG = 1,
    C_SHARP = 2,
    D_REG = 3
};

#endif  //dont forget this line!

Such guards ensure that the content of the header file will be included once in one translation unit (TU).

If your compiler supports (modern compilers support this), you could use #pragma once as:

//custom_types.h

#pragma once  //it ensures that the content of this header will be 
              //included once in one translation unit

enum playback_type {
    NOTE_PB,
    SONG_PB
};

enum note_name {
    C_REG = 1,
    C_SHARP = 2,
    D_REG = 3
};