syscalls.c

在linux下多媒体开发实例linux下多媒体开发

/*
 * syscalls.c
 * Program to illustrate common system calls. Doesn't actually
 * perform any useful function, but will later be expanded into
 * a program which does.
 */

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <linux/soundcard.h>

int main()
{
  int fd;	            /* device file descriptor */
  int arg;	            /* argument for ioctl call */
  unsigned char buf[1000];  /* buffer to hold data */
  int status;               /* return status of system calls */

  /* open device */
  status = fd = open("/dev/dsp", O_RDWR);
  if (status == -1) {
    perror("error opening /dev/dsp");
    exit(1);
  }

  /* set a parameter using ioctl call */
  arg = 8000; /* sampling rate */
  status = ioctl(fd, SOUND_PCM_WRITE_RATE, &arg);
  if (status == -1) {
    perror("error from SOUND_PCM_WRITE_RATE ioctl");
    exit(1);
  }

  /* read some data */
  status = read(fd, buf, sizeof(buf));
  if (status == -1) {
    perror("error reading from /dev/dsp");
    exit(1);
  }

  /* write some data */
  status = write(fd, buf, sizeof(buf));
  if (status == -1) {
    perror("error writing to /dev/dsp");
    exit(1);
  }

  /* close the device */
  status = close(fd);
  if (status == -1) {
    perror("error closing /dev/dsp");
    exit(1);
  }

  /* and exit */
  return(0);
}