利用alsa 完成linux下音频采集，第一次用C++写程序，很菜，很水，记录下当时的水平，以后肯定会有提高，算是一个纪念吧

1、运行时前先装库,sudo apt-get install libalsa
2遍tab自动提示出库文件，选择库，alsa-ocaml-dev，最终的命令行为：sudo apt-get install libalsa-ocaml-dev
2、编译执行脚本，gcc -o main main.c -lasound;
3、执行 ./main
以下是代码`#define LSA_PCM_NEW_HW_PARAMS_API
#include <stdlib.h>
#include <stdio.h>
#include <alsa/asoundlib.h>
#include <signal.h>
static int recording;

void stop_record(int param)
{
recording = 0;
}
void InitCapture(snd_pcm_t ** handle,snd_pcm_hw_params_t ** params,snd_pcm_uframes_t* frames,char ** buffer,int* size)
{
int ret;
unsigned int val;
int dir;
//打开设备
ret = snd_pcm_open(handle, “default”, SND_PCM_STREAM_CAPTURE, 0);
printf(“after open file\n”);
if (ret < 0)
{
fprintf(stderr, “unable to open device:%s\n”, snd_strerror(ret));
exit(1);
}
//分配一个硬件参数结构体
snd_pcm_hw_params_alloca(params);

//使用默认参数
snd_pcm_hw_params_any(*handle, *params);

//翻译
    snd_pcm_hw_params_set_access(*handle, *params, SND_PCM_ACCESS_RW_INTERLEAVED);

//S16小端
snd_pcm_hw_params_set_format(*handle, *params, SND_PCM_FORMAT_S16_LE);

//双通道，立体声
snd_pcm_hw_params_set_channels(*handle, *params, 2);

//采样率
val = 44100;
snd_pcm_hw_params_set_rate_near(*handle, *params,&val,&dir);

*frames = 32;
snd_pcm_hw_params_set_period_size_near(*handle, *params,frames,&dir);

//参数生效
ret = snd_pcm_hw_params(*handle, *params);
if (ret<0)
{
	fprintf(stderr, "unable to set hw parameters:%s\n", snd_strerror(ret));
		exit(1);
}
//得到一个周期的数据大小
snd_pcm_hw_params_get_period_size(*params, frames, &dir);

//16位双通道，16位为2字节，2字节*2通道=4，假如frames=1024，则size是1024*4 = 4096
*size = *frames * 4;
*buffer = (char*)malloc(*size); 

//设置一个周期的时间长度
snd_pcm_hw_params_get_period_time(*params, &val, &dir);

}

void CaptureAudio(snd_pcm_t ** handle,snd_pcm_uframes_t* frames,char ** buffer,int* size,FILE ** pFile)
{
int ret;

recording = 1;
while (recording)
{
	ret = snd_pcm_readi(*handle, *buffer,*frames);
	if (ret == -EPIPE )
	{
		fprintf(stderr, "overrun occurred\n");
		snd_pcm_prepare(*handle);
	}
	else if (ret < 0)
	{
		fprintf(stderr, "error from read\n");
		snd_strerror(ret);
	}
	else if (ret != (int)(*frames))
	{
		fprintf(stderr, "short read %d frames\n",ret);
	}
	printf("write to file......%d\n", *size);
	//写到标准输出中去
	ret = fwrite(*buffer, sizeof(char), *size, *pFile);
	if (ret != *size)
	{
		fprintf(stderr, "short write :write %d bytes\n", ret);
	}
	if (signal(SIGINT, stop_record)==SIG_ERR)
	{
		fprintf(stderr, "signal failed\n");
	}
}

}

void CloseCaptureDevice(FILE ** pFile,snd_pcm_t ** handle,char ** buffer)
{
printf(“write file exit\n”);
snd_pcm_drain(*handle);
snd_pcm_close(*handle);
free(*buffer);
fclose(*pFile);
}

int main()
{
FILE * pFile;
pFile = fopen(“test.pcm”, “wb”);
int size;
//给文件操作分配一个句柄
snd_pcm_t * handle;
//硬件参数
snd_pcm_hw_params_t * params;
//
snd_pcm_uframes_t frames;
char * buffer;
printf(“before open file\n”);
InitCapture(&handle,&params,&frames,&buffer,&size);
CaptureAudio(&handle,&frames,&buffer,&size,&pFile);
CloseCaptureDevice(&pFile,&handle,&buffer);
printf(“write file exit\n”);

return 0;

}
`