c - 我的代码有什么问题？我得到一个 "Bus Error"

Question

我正在尝试读取包含原始音频的文件并使用 FLAC 对其进行编码.当我运行该程序时，出现“总线错误”。有什么问题吗？
我正在使用以下行在 OS X 10.6.8 上进行编译:

gcc nsFlacEncoder.c -I/opt/local/include -lflac -m32 -o flac_enc

#include "FLAC/stream_encoder.h"
#define READSIZE 40000
char buffer[READSIZE];
FLAC__int32 pcm[READSIZE/2];

FLAC__StreamEncoderWriteStatus write_callback(const FLAC__StreamEncoder *encoder, const  FLAC__byte buffer[], size_t bytes, unsigned samples, unsigned current_frame, void *client_data)
{
    FILE * fp;
    fp = fopen("rec.flac","rw");
    fwrite(buffer, 1, bytes, fp);
    fclose(fp);
    return 0;
}

int rawToFlac()
{
    FLAC__bool ok = true;
    FLAC__StreamEncoder *encoder = 0;
    FLAC__StreamEncoderInitStatus init_status;
    unsigned sample_rate = 16000;
    unsigned channels = 1;
    unsigned bps = 16;

    if((encoder=FLAC__stream_encoder_new()) == NULL){
        printf("Error!");
        return 1;
    }

    ok &= FLAC__stream_encoder_set_verify(encoder, true);
    ok &= FLAC__stream_encoder_set_compression_level(encoder, 5);
    ok &= FLAC__stream_encoder_set_channels(encoder, channels);
    ok &= FLAC__stream_encoder_set_bits_per_sample(encoder, bps);
    ok &= FLAC__stream_encoder_set_sample_rate(encoder, sample_rate);
    ok &= FLAC__stream_encoder_set_total_samples_estimate(encoder, READSIZE);

    if(ok){
        init_status = FLAC__stream_encoder_init_stream(encoder, &write_callback, NULL, NULL, NULL, /*client_data=*/NULL);
        if(init_status != FLAC__STREAM_ENCODER_INIT_STATUS_OK){
            printf("Encoder not initiated");
            return 1;
        }
    }

    if(ok){
        while(ok)
        {       
            /* convert the packed little-endian 16-bit PCM samples from WAVE into an interleaved FLAC__int32 buffer for libFLAC */
            size_t i;
            for(i = 0; i < 20000; i++) {
                /* inefficient but simple and works on big- or little-endian machines */
                pcm[i] = (FLAC__int32)(((FLAC__int16)(FLAC__int8)buffer[2*i+1] << 8) | (FLAC__int16)buffer[2*i]);
            }
            /* feed samples to encoder */
            ok = FLAC__stream_encoder_process_interleaved(encoder, pcm, 20000);
        }
    }

    ok &= FLAC__stream_encoder_finish(encoder);
    printf("Finished.");

    FLAC__stream_encoder_delete(encoder);   
    return 0;
}

int main()
{

    FILE *file;
    file = fopen("recording","rb");
    fread(buffer,2, 20000, file);
    rawToFlac();
    fclose(file);
    return 0;
}

运行 gdb flac_enc 给我这个:

warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/bitmath.o" - no debug information available for "bitmath.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/bitreader.o" - no debug information available for "bitreader.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/bitwriter.o" - no debug information available for "bitwriter.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/cpu.o" - no debug information available for "cpu.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/crc.o" - no debug information available for "crc.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/fixed.o" - no debug information available for "fixed.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/format.o" - no debug information available for "format.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/lpc.o" - no debug information available for "lpc.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/md5.o" - no debug information available for "md5.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/memory.o" - no debug information available for "memory.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/metadata_iterators.o" - no debug information available for "metadata_iterators.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/metadata_object.o" - no debug information available for "metadata_object.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/stream_decoder.o" - no debug information available for "stream_decoder.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/stream_encoder.o" - no debug information available for "stream_encoder.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/stream_encoder_framing.o" - no debug information available for "stream_encoder_framing.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/window.o" - no debug information available for "window.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/ogg_decoder_aspect.o" - no debug information available for "ogg_decoder_aspect.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/ogg_encoder_aspect.o" - no debug information available for "ogg_encoder_aspect.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/ogg_helper.o" - no debug information available for "ogg_helper.c".
warning: Could not find object file "/Users/benski/Desktop/flac-1.2.1/src/libFLAC/.libs/ogg_mapping.o" - no debug information available for "ogg_mapping.c".

这很奇怪，因为我的系统上没有用户“benski”。但我确定 FLAC 库已正确安装为 example programs完美运行。

Answer 1

在 main() 中，您不检查文件是否已成功打开。问题可能在于您在 fread() 操作中使用了空指针。同样，在 write_callback() 函数中，您的代码显示了无敌假设。 (此外，如果您的回调被调用不止一次，则第二次调用会覆盖第一次调用产生的数据。但是，这是一个不同的问题。)

您不检查 fread() 读取了多少个 2 字节单元。您也不检查 fwrite() 写入了多少数据 - 它是否成功？

您应该能够使用 gdb 或类似的调试器来查看错误发生的位置。

您也可以使用 valgrind 来发现问题。

您不需要同时使用 if 和 while:

if (ok)
{
    while (ok)
    {
        ...
    }
}

只有循环就足够了；如果 ok 在第一个循环中为 false，它将执行零次。如果在 while 循环之后和 if 结束之前有一个语句，那么两者都是必需的。

通常，当您尝试访问未对齐的数据对象时，RISC 芯片上会发生 SIGBUS(总线错误)。目前尚不清楚哪一行可能导致此代码中的问题。尽管之前有关于“空指针”的评论，但通常以 SIGSEGV(分段违规)而不是 SIGBUS 结束。