Cannot #include some classes

[wysota]

I doubt if that iwould make any difference. Whatever the order, when the errors occur those includes have all been included.

It does make a difference. Consider the following example:

// file1.h
#ifndef X
#define X int
#endif

// file1.h
#ifndef X
#define X int
#endif

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// file2.h
#ifndef X
#define X std::string
#endif

// file2.h
#ifndef X
#define X std::string
#endif

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and then two orders of inclusion:

// main.cpp
#include "file1.h"
#include "file2.h"
//...
X x;

// main.cpp
#include "file1.h"
#include "file2.h"
//...
X x;

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// main.cpp
#include "file2.h"
#include "file1.h"
// ...
X x;

// main.cpp
#include "file2.h"
#include "file1.h"
// ...
X x;

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Now in version 1 "x" will be of type "int" but in version 2 it will be of type "std::string". So the order may matter (in a place AFTER the files have been included - when "x" is declared).

Try reordering the includes and try to substitute all the includes you can with forward declarations.

[Jayes]

Try reordering the includes and try to substitute all the includes you can with forward declarations.

Wysota, you are not just a master of Zen...

I tried many permutations and found that, in qm_player.h

this does not workt:

#include "qm_config.h"
#include "qm_tracks.h"

and this works fine:

#include "qm_tracks.h"
#include "qm_config.h"

The culprit is

#include <X11/Xlib.h>

in qm_config.h. It is something I can do without, so I removed it. Now I can put qm_tracks.h where I please.

Well, I learned something today. Thank you very much indeed!

--
jayes

[norobro]

Jayes,

I didn't think that the include order of header files made any difference either. Wysota's explanation cleared that up for me. Anyway I was browsing around in the sources and found this in qcoreevent.h:

enum Type {
        /*
          If you get a strange compiler error on the line with None,
          it's probably because you're also including X11 headers,
          which #define the symbol None. Put the X11 includes after
          the Qt includes to solve this problem.
        */
        None = 0,                               // invalid event

enum Type {
        /*
          If you get a strange compiler error on the line with None,
          it's probably because you're also including X11 headers,
          which #define the symbol None. Put the X11 includes after
          the Qt includes to solve this problem.
        */
        None = 0,                               // invalid event

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It would have been nice if that comment was in qstyleoption.h, huh?
Norm

[squidge]

IMO, It's just another reason why you should never have such ambiguous symbols in your code base. I dislike code which is like this (Although I don't avoid such code unless it's small or easily rewritten). Either put the enum in a class, or prefix it with the subsystem its involved with. Eg. if "None" is associated with the event code, then it should be named "QtEvent_None".