我正在OS X系统上编译openAL工具，并且在构建示例文件时遇到了麻烦。 我收到了错误：
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
(maybe you meant: _SDL_main)
ld: symbol(s) not found for architecture x86_64
在Linux机器上编译时，我没有错误，示例二进制文件工作正常。我究竟做错了什么？
这是我正在编译的程序的代码：
#include <stdio.h>
#include <assert.h>
#include <math.h>
#include "AL/al.h"
#include "AL/alc.h"
#include "AL/alext.h"
#include "common/alhelpers.h"
#include "common/sdl_sound.h"
#ifndef M_PI
#define M_PI (3.14159265358979323846)
#endif
static LPALCGETSTRINGISOFT alcGetStringiSOFT;
static LPALCRESETDEVICESOFT alcResetDeviceSOFT;
/* LoadBuffer loads the named audio file into an OpenAL buffer object, and
* returns the new buffer ID. */
static ALuint LoadSound(const char *filename)
{
ALenum err, format, type, channels;
ALuint rate, buffer;
size_t datalen;
void *data;
FilePtr sound;
/* Open the audio file */
sound = openAudioFile(filename, 1000);
if(!sound)
{
fprintf(stderr, "Could not open audio in %s\n", filename);
closeAudioFile(sound);
return 0;
}
/* Get the sound format, and figure out the OpenAL format */
if(getAudioInfo(sound, &rate, &channels, &type) != 0)
{
fprintf(stderr, "Error getting audio info for %s\n", filename);
closeAudioFile(sound);
return 0;
}
format = GetFormat(channels, type, NULL);
if(format == AL_NONE)
{
fprintf(stderr, "Unsupported format (%s, %s) for %s\n",
ChannelsName(channels), TypeName(type), filename);
closeAudioFile(sound);
return 0;
}
/* Decode the whole audio stream to a buffer. */
data = decodeAudioStream(sound, &datalen);
if(!data)
{
fprintf(stderr, "Failed to read audio from %s\n", filename);
closeAudioFile(sound);
return 0;
}
/* Buffer the audio data into a new buffer object, then free the data and
* close the file. */
buffer = 0;
alGenBuffers(1, &buffer);
alBufferData(buffer, format, data, datalen, rate);
free(data);
closeAudioFile(sound);
/* Check if an error occured, and clean up if so. */
err = alGetError();
if(err != AL_NO_ERROR)
{
fprintf(stderr, "OpenAL Error: %s\n", alGetString(err));
if(buffer && alIsBuffer(buffer))
alDeleteBuffers(1, &buffer);
return 0;
}
return buffer;
}
int main(int argc, char **argv)
{
ALCdevice *device;
ALuint source, buffer;
const char *soundname;
const char *hrtfname;
ALCint hrtf_state;
ALCint num_hrtf;
ALdouble angle;
ALenum state;
/* Print out usage if no file was specified */
if(argc < 2 || (strcmp(argv[1], "-hrtf") == 0 && argc < 4))
{
fprintf(stderr, "Usage: %s [-hrtf <name>] <soundfile>\n", argv[0]);
return 1;
}
/* Initialize OpenAL with the default device, and check for HRTF support. */
if(InitAL() != 0)
return 1;
if(strcmp(argv[1], "-hrtf") == 0)
{
hrtfname = argv[2];
soundname = argv[3];
}
else
{
hrtfname = NULL;
soundname = argv[1];
}
device = alcGetContextsDevice(alcGetCurrentContext());
if(!alcIsExtensionPresent(device, "ALC_SOFT_HRTF"))
{
fprintf(stderr, "Error: ALC_SOFT_HRTF not supported\n");
CloseAL();
return 1;
}
/* Define a macro to help load the function pointers. */
#define LOAD_PROC(d, x) ((x) = alcGetProcAddress((d), #x))
LOAD_PROC(device, alcGetStringiSOFT);
LOAD_PROC(device, alcResetDeviceSOFT);
#undef LOAD_PROC
/* Enumerate available HRTFs, and reset the device using one. */
alcGetIntegerv(device, ALC_NUM_HRTF_SPECIFIERS_SOFT, 1, &num_hrtf);
if(!num_hrtf)
printf("No HRTFs found\n");
else
{
ALCint attr[5];
ALCint index = -1;
ALCint i;
printf("Available HRTFs:\n");
for(i = 0;i < num_hrtf;i++)
{
const ALCchar *name = alcGetStringiSOFT(device, ALC_HRTF_SPECIFIER_SOFT, i);
printf(" %d: %s\n", i, name);
/* Check if this is the HRTF the user requested. */
if(hrtfname && strcmp(name, hrtfname) == 0)
index = i;
}
i = 0;
attr[i++] = ALC_HRTF_SOFT;
attr[i++] = ALC_TRUE;
if(index == -1)
{
if(hrtfname)
printf("HRTF \"%s\" not found\n", hrtfname);
printf("Using default HRTF...\n");
}
else
{
printf("Selecting HRTF %d...\n", index);
attr[i++] = ALC_HRTF_ID_SOFT;
attr[i++] = index;
}
attr[i] = 0;
if(!alcResetDeviceSOFT(device, attr))
printf("Failed to reset device: %s\n", alcGetString(device, alcGetError(device)));
}
/* Check if HRTF is enabled, and show which is being used. */
alcGetIntegerv(device, ALC_HRTF_SOFT, 1, &hrtf_state);
if(!hrtf_state)
printf("HRTF not enabled!\n");
else
{
const ALchar *name = alcGetString(device, ALC_HRTF_SPECIFIER_SOFT);
printf("HRTF enabled, using %s\n", name);
}
fflush(stdout);
/* Load the sound into a buffer. */
buffer = LoadSound(soundname);
if(!buffer)
{
CloseAL();
return 1;
}
/* Create the source to play the sound with. */
source = 0;
alGenSources(1, &source);
alSourcei(source, AL_SOURCE_RELATIVE, AL_TRUE);
alSource3f(source, AL_POSITION, 0.0f, 0.0f, -1.0f);
alSourcei(source, AL_BUFFER, buffer);
assert(alGetError()==AL_NO_ERROR && "Failed to setup sound source");
/* Play the sound until it finishes. */
angle = 0.0;
alSourcePlay(source);
do {
al_nssleep(10000000);
/* Rotate the source around the listener by about 1/4 cycle per second.
* Only affects mono sounds.
*/
angle += 0.01 * M_PI * 0.5;
alSource3f(source, AL_POSITION, (ALfloat)sin(angle), 0.0f, -(ALfloat)cos(angle));
alGetSourcei(source, AL_SOURCE_STATE, &state);
} while(alGetError() == AL_NO_ERROR && state == AL_PLAYING);
/* All done. Delete resources, and close OpenAL. */
alDeleteSources(1, &source);
alDeleteBuffers(1, &buffer);
CloseAL();
return 0;
}
这是链接器命令（由cmake自动生成）：
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc -std=c11 -O2 -g -D_DEBUG -Wl,-search_paths_first -Wl,-headerpad_max_install_names CMakeFiles/alhrtf.dir/examples/alhrtf.c.o -o alhrtf libex-common.a /usr/local/lib/libSDL_sound.dylib -framework SDL2 -framework Cocoa -framework SDL2 -framework Cocoa libcommon.a libopenal.1.17.2.dylib libcommon.a -framework AudioToolbox -framework ApplicationServices -framework AudioUnit -framework CoreAudio -lpthread -ldl -lm -pthread -Wl,-rpath,/Library/Frameworks -Wl,-rpath,/Users/tschekar/Downloads/openal-soft/cmake