问C:为什么我的库中的全局变量不会更新？(使用ALSA库)
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Stack Overflow用户

提问于 2019-05-23 05:11:32

回答 1查看 41关注 0票数 0

前言：我看过其他的答案，我相信这是一个不同类型的问题。这可能与指针有关，但其他答案都没有帮助。我也可能遗漏了一些东西。

我设法使用ALSA库编写了一个将原始音频数据流式传输到stdout的工作程序。我现在正在尝试将这段代码泛化到一个库中，并且库的.c文件中的全局变量没有更新。据我所知，设置与原始程序没有什么不同，所以我认为它应该可以工作……但事实并非如此。如果有人能解释清楚我是怎么把事情搞砸的，我会很感激的。抢先谢谢你！

EDIT 1:

调用wm8782_open_audio()时，wm8782.c顶部的所有全局变量都无法设置。例如，在调用wm8782_open_audio()之后在wm8782_us_to_loops()中调用snd_pcm_hw_params_get_period_time(params, &val, &dir);时，会因为params未初始化而失败。但是，wm8782_open_audio()完成时没有错误！

EDIT 2:

我在我的头中添加了extern声明，没有骰子。有关更新的文件，请参阅下面的内容。

EDIT 3:

我已经在一个没有头文件的C文件中重现了这个问题。简单地将代码分解成函数就足以将其分解。我已经用这个整体的C文件替换了这两个库文件，以消除链接器错误等。

这是我试图将其推广到库中的原始程序。这就像我想要的那样工作。

#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>

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;

int main()
{
    /* Open PCM device for recording (capture). */
    rc = snd_pcm_open(&handle, "hw:1",
                      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 32-bit little-endian format */
    snd_pcm_hw_params_set_format(handle, params,
                                 SND_PCM_FORMAT_S32_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 64 frames. */
    frames = 64;
    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 * 8; /* 4 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);
    //fprintf(stderr, "%u\n", val);
    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;
}

现在这里是模块化版本，它最终将成为一个库。对于ERROR: Failed to get number of loops.，此操作失败

#define ALSA_PCM_NEW_HW_PARAMS_API

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <alsa/asoundlib.h>

char *wm8782_buffer;
int wm8782_buffer_size;

snd_pcm_t *wm8782_handle;
snd_pcm_hw_params_t *wm8782_params;
int wm8782_dir;
snd_pcm_uframes_t wm8782_frames;
unsigned int wm8782_val;
int wm8782_rc;

typedef enum
{
    WM8782_READ_OVERRUN,
    WM8782_READ_ERROR,
    WM8782_READ_SHORT,
    WM8782_READ_GOOD,
} wm8782read_t;

typedef enum
{
    WM8782_RATE_8K = 8000,
    WM8782_RATE_16K = 16000,
    WM8782_RATE_32K = 32000,
    WM8782_RATE_44_1K = 44100,
    WM8782_RATE_48K = 48000,
    WM8782_RATE_96K = 96000,
    WM8782_RATE_192K = 192000,
} wm8782rate_t;

bool wm8782_open_audio(wm8782rate_t rate_in, snd_pcm_uframes_t wm8782_frames_in)
{
    // Open PCM device for recording (capture).
    wm8782_rc = snd_pcm_open(&wm8782_handle, "hw:1",
                      SND_PCM_STREAM_CAPTURE, 0);
    if (wm8782_rc < 0)
    {
        fprintf(stderr,
                "ERROR: Unable to open pcm device: %s\n",
                snd_strerror(wm8782_rc));
        return false;
    }

    // Allocate a hardware parameters object.
    snd_pcm_hw_params_alloca(&wm8782_params);

    // Fill it in with default values
    snd_pcm_hw_params_any(wm8782_handle, wm8782_params);

    // Set the desired hardware parameters. */

    // Interleaved mode
    snd_pcm_hw_params_set_access(wm8782_handle, wm8782_params, SND_PCM_ACCESS_RW_INTERLEAVED);

    // Signed 32-bit little-endian format
    snd_pcm_hw_params_set_format(wm8782_handle, wm8782_params, SND_PCM_FORMAT_S32_LE);

    // Two channels (stereo)
    snd_pcm_hw_params_set_channels(wm8782_handle, wm8782_params, 2);

    // Set rate
    wm8782_val = rate_in;
    snd_pcm_hw_params_set_rate_near(wm8782_handle, wm8782_params, &wm8782_val, &wm8782_dir);

    // Set period size.
    wm8782_frames = wm8782_frames_in;
    snd_pcm_hw_params_set_period_size_near(wm8782_handle, wm8782_params, &wm8782_frames, &wm8782_dir);

    // Write the parameters to the driver
    wm8782_rc = snd_pcm_hw_params(wm8782_handle, wm8782_params);
    if (wm8782_rc < 0)
    {
        fprintf(stderr,
                "ERROR: Unable to set hw parameters: %s\n",
                snd_strerror(wm8782_rc));
        return false;
    }

    // Use a buffer large enough to hold one period
    snd_pcm_hw_params_get_period_size(wm8782_params, &wm8782_frames, &wm8782_dir);
    wm8782_buffer_size = wm8782_frames * 8; // 4 bytes/sample, 2 channels
    wm8782_buffer = (char *) malloc(wm8782_buffer_size);

    return true;
}

void wm8782_close_audio()
{
    snd_pcm_drain(wm8782_handle);
    snd_pcm_close(wm8782_handle);
    free(wm8782_buffer);
}

wm8782read_t wm8782_read_audio()
{
    wm8782_rc = snd_pcm_readi(wm8782_handle, wm8782_buffer, wm8782_frames);
    if (wm8782_rc == -EPIPE)
    {
        // EPIPE means overrun
        fprintf(stderr, "ERROR: Overrun occurred\n");
        snd_pcm_prepare(wm8782_handle);
        return WM8782_READ_OVERRUN;
    }
    else if (wm8782_rc < 0)
    {
        fprintf(stderr, "ERROR: From read: %s\n", snd_strerror(wm8782_rc));
        return WM8782_READ_ERROR;
    }
    else if (wm8782_rc != (int)wm8782_frames)
    {
        fprintf(stderr, "ERROR: Short read, read %d wm8782_frames\n", wm8782_rc);
        return WM8782_READ_SHORT;
    }

    return WM8782_READ_GOOD;
}

unsigned int wm8782_us_to_loops(unsigned int us_in)
{
    if(snd_pcm_hw_params_get_period_time(wm8782_params, &wm8782_val, &wm8782_dir) < 0)
    {
        fprintf(stderr, "ERROR: Failed to get number of loops.\n");
        return 0;
    }
    //fprintf(stderr, "%u\n", wm8782_val);
    return (us_in / wm8782_val);
}

int main()
{
    if(!wm8782_open_audio(44100, 64))
    {
        fprintf(stderr, "unable to open pcm device");
    }

    unsigned int loops =  wm8782_us_to_loops(5000000);

    while (loops > 0)
    {
        loops--;
        wm8782_read_audio();

        wm8782_rc = write(1, wm8782_buffer, wm8782_buffer_size);
        if (wm8782_rc != wm8782_buffer_size)
            fprintf(stderr,
                    "short write: wrote %d bytes\n", wm8782_rc);
    }

    wm8782_close_audio();

    return 0;
}

global-variables

alsa

libasound

回答 1

Stack Overflow用户

发布于 2019-05-23 07:16:09

好的，事实证明这根本不是一个全球性的问题…抱歉，各位！它是传递给snd_pcm_hw_params_get_period_size()的一些奇怪的无效参数。代码实际上使用了手动定义的循环数量，所以我要结束这个问题。

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/56265081

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问C:为什么我的库中的全局变量不会更新？(使用ALSA库)
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