c++ - 未知类型名称错误

Question

Note我确信这是显而易见的，但我只是看不到它：当我尝试使用我的类（非常频繁地使用）时，xcode 突然给我各种错误。

下面是类头的样子：

class Note : public Playable{

private:

public:

    double theta;
    double frequency;
    int duration; 
    int startTime; // tussen 1 en 32
    int measureNumber;
    float velocity;
    Playable *track;
    virtual float getValue();

    static double calculateNoteFrequency(int aOctaveNumber, note_name aNoteName);

    Note(double aFreq, float aVelocity, int aDuration, int aMeasureNumber, int aStarttimeInsideMeasure, Playable *aTrack){
//      theta = 0;
        Note();
        frequency = aFreq;
        duration = aDuration;
        velocity = aVelocity;
        measureNumber = aMeasureNumber;
        startTime = aStarttimeInsideMeasure;
        track = aTrack;
    }

    Note(){
        theta = 0;
    }
    void toString();

};

编辑

这是完整的编译器错误消息：

In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.cpp:9:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.h:14:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:16:
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:19:12: error: use of undeclared identifier 'Note'
    vector<Note> notelist;
           ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:19:18: error: C++ requires a type specifier for all declarations
    vector<Note> notelist;
                 ^~~~~~~~
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:23:12: error: use of undeclared identifier 'Note'
    vector<Note> getNotelist();
           ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:23:18: error: C++ requires a type specifier for all declarations
    vector<Note> getNotelist();
                 ^~~~~~~~~~~
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:24:18: error: unknown type name 'Note'
    void addNote(Note const &note){
                 ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:24:23: error: expected ')'
    void addNote(Note const &note){
                      ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Pattern.h:24:17: note: to match this '('
    void addNote(Note const &note){
                ^
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.cpp:9:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.h:14:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:17:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Synth.h:11:
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Oscillator.h:21:18: error: unknown type name 'Note'
    void setNote(Note &aNote);
                 ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Oscillator.h:23:20: error: unknown type name 'Note'
    float getValue(Note &note);
                   ^
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.cpp:9:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.h:14:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:17:
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Synth.h:47:21: error: unknown type name 'Note'
    float getSample(Note &note);
                    ^
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.cpp:9:
In file included from /Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Note.h:14:
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:30:17: error: use of undeclared identifier 'Note'
        multimap<long, Note> noteList;
                       ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:30:23: error: C++ requires a type specifier for all declarations
        multimap<long, Note> noteList;
                             ^~~~~~~~
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:33:2: error: unknown type name 'Note'
        Note &addNoteAndReturnReference(Note &note);
        ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:33:34: error: unknown type name 'Note'
        Note &addNoteAndReturnReference(Note &note);
                                        ^
/Users/osxursnm/Development/SynthSequencer2/SynthSequencer2/Track.h:34:18: error: unknown type name 'Note'
        void removeNote(Note &note);
                        ^
14 errors generated.

Answer 1

我的猜测是你有一个交叉引用的问题。

在Note.h您包括Track.hwhich 使用类型的对象Note。Note在Track.h文件中使用前向声明并Note.h仅将文件包含在Track.cpp.

所以尝试

class Note;

Track在文件中声明类之前Track.h并删除文件#include "Note.h"开头的语句。