La conversión .mm causa símbolos indefinidos para la arquitectura Errores de i386

Question

Recientemente importé un archivo C++ en mi proyecto obj que quiero usar. En la clase que quiero usar, cambio el nombre del archivo de MyClass.m a MyClass.mm.

Hacer esto me da 20 o más errores. ¿Qué significan exactamente estos errores y cómo puedo cambiar MyClass a una clase objetiva de C++ para facilitar la nueva clase de C++ que deseo utilizar, sin obtener estos errores?

Undefined symbols for architecture i386: 
    "setAudioInputIsStereo(audiosourceobj*, bool)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "setAudioInputFrameCount(audiosourceobj*, int)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "setAudioInputSendValue(audiosourceobj*, int)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "getPointerToAudioLeftBuffer(audiosourceobj*)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "getPointerToAudioRightBuffer(audiosourceobj*)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "freeAudioBuffers(audiosourceobj*)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
    "setAudioInputReadPoint(audiosourceobj*, int)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
    "setAudioInputHasAudio(audiosourceobj*, bool)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
     -[Engine reset] in Engine.o 
     -[Engine setAudioPath:channel:pad:] in Engine.o 
    "setAudioInputState(audiosourceobj*, int)", referenced from: 
     -[Engine extractMp3Audio:withChannelId:withPadId:] in Engine.o 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
     -[Engine setAudioPath:channel:pad:] in Engine.o 
    "initAudioInputHasAudio(audiosourceobj*, signed char)", referenced from: 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
    "initAudioInputReadPoint(audiosourceobj*, int)", referenced from: 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
    "initAudioInputFrameCount(audiosourceobj*, int)", referenced from: 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
    "initAudioInputSampleToAction(audiosourceobj*, int)", referenced from: 
     -[Engine clearAudioInput:pid:] in Engine.o 
     -[Engine reset] in Engine.o 
    "newChannelOBJ()", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "setVolume(channelobj*, float)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "setMute(channelobj*, int)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "setNumberOfInputs(channelobj*, int)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "setChannelID(channelobj*, int)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "createInputs(channelobj*, int)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "setBufferSize(channelobj*, float)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "createChannelEQS(channelobj*)", referenced from: 
     setUpChannels(int, int)in Engine.o 
    "actionupdatecomplete(audiosourceobj*, objc_object*)", referenced from: 
     channelMixerCallback(void*, unsigned long*, AudioTimeStamp const*, unsigned long, unsigned long, AudioBufferList*)in Engine.o 

Answer 1

Parece que sus funciones tienen una vinculación C, pero no las ha declarado correctamente en su encabezado. Entonces, un archivo .mm (Objective-C++) los verá y asumirá el enlace C++. La solución más fácil es envolver que #include declaración en la apropiada extern bloque:

extern "C" { 
    #include "..." 
} 

Una mejor solución es hacer que dentro de la cabecera sí:

#if defined(__cplusplus) 
    extern "C" { 
#endif /* defined(__cplusplus) */ 

extern void whatever(void); 
extern int foobar(double); 
... 

#if defined(__cplusplus) 
    } 
#endif /* defined(__cplusplus) */ 

Apple utiliza macros para esto, muy bien nombrado __BEGIN_DECLS y __END_DECLS pero no son estándares, por lo que no puede usarlos directamente en archivos compartidos entre plataformas.