Question

我最近将一个c ++文件导入到我想要使用的obj项目中。在我想要使用它的类中，我将文件名从MyClass.m更改为MyClass.mm。

这样做会给我20个左右的错误。这些错误究竟是什么意思，我如何将MyClass更改为一个客观的c ++类来促进我想要使用的新c ++类，而不会出现这些错误？

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

听起来您的函数具有C链接，但您尚未在其标题中正确声明。因此.mm文件（Objective-C ++）将会看到它们并假设C ++链接。最简单的解决方法是将#include语句包装在适当的extern块中：

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

更好的解决方案是在标题内执行此操作：

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

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

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

Apple为此使用宏，名称很好__BEGIN_DECLS和__END_DECLS，但它们是非标准的，因此您无法直接在跨平台共享的文件中使用它们。

.mm转换导致架构i386错误的未定义符号

1 个答案: