c - 添加新代码时程序停止工作

Question

我正在尝试使用此 C 代码通过 ALSA API 捕获数据:

#define ALSA_PCM_NEW_HW_PARAMS_API

#include <alsa/asoundlib.h>

int main() {
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int val;
int dir;
snd_pcm_uframes_t frames;
char *buffer;

/* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, "default",
                SND_PCM_STREAM_CAPTURE, 0);
if (rc < 0) {
fprintf(stderr,
        "unable to open pcm device: %s\n",
        snd_strerror(rc));
exit(1);
}

/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(&params);

/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);

/* Set the desired hardware parameters. */

/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params,
                  SND_PCM_ACCESS_RW_INTERLEAVED);

/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params,
                          SND_PCM_FORMAT_S16_LE);

/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 2);

/* 44100 bits/second sampling rate (CD quality) */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params,
                              &val, &dir);

/* Set period size to 32 frames. */
frames = 32;
snd_pcm_hw_params_set_period_size_near(handle,
                          params, &frames, &dir);

/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
fprintf(stderr,
        "unable to set hw parameters: %s\n",
        snd_strerror(rc));
  exit(1);
}

/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params,
                                  &frames, &dir);
size = frames * 4; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);

/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params,
                                     &val, &dir);
loops = 5000000 / val;

while (loops > 0) {
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE) {
  /* EPIPE means overrun */
  fprintf(stderr, "overrun occurred\n");
  snd_pcm_prepare(handle);
} else if (rc < 0) {
  fprintf(stderr,
          "error from read: %s\n",
          snd_strerror(rc));
} else if (rc != (int)frames) {
  fprintf(stderr, "short read, read %d frames\n", rc);
}
rc = write(1, buffer, size);
if (rc != size)
  fprintf(stderr,
          "short write: wrote %d bytes\n", rc);
}

snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);

return 0;
}

所以代码实际上是有效的，但是如果我在“while (loops > 0)”中添加另一个循环，例如:

int i;
for(i=0;i<128;i++){
printf("I: %i \n", i);
}

程序的输出将是:

unable to set hw parameters: Invalid argument

我真的不明白最后一个简单的循环如何影响开头的程序？有谁知道如何修复/防止该错误？非常感谢!

Answer 1

错误无法设置硬件参数:参数无效不是由于您的附加代码片段造成的。错误的实际原因是未初始化的 dir 变量。要解决该问题，您必须正确初始化 dir 或传递 0 或 NULL 而不是 &dir 。