FIFO: communication between two process

為了控制另一個程式的執行，這個範例用了pipe的方式，兩個程式之間用pipe來溝通（不過是單向），利用這種方式，我們就可以很簡單的控制另一個程式的執行。

r.c: read date.
w.c: write data.

r.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>

#define FIFO_NAME "/tmp/my_fifo"
#define BUFFER_SIZE PIPE_BUF

int main(int argc, char *argv[])
{
  int res;
  int open_mode = 0;
  int n=0;
  char MYkey;
  open_mode= O_RDONLY | O_NONBLOCK;  //是nonblock的

  if (access(FIFO_NAME, F_OK) == -1) {
      res = mkfifo(FIFO_NAME, 0777);
      if (res != 0) {
          fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME);
          exit(EXIT_FAILURE);
      }
  }

  res = open(FIFO_NAME, open_mode);
  while(1)
  {
   n=read(res,&MYkey,BUFFER_SIZE);
   if(n>0)
    printf("%c\n",MYkey);
   else
    printf("No Data.\n");
   sleep(1);
  }
  exit(EXIT_SUCCESS);
}

w.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>

#define FIFO_NAME "/tmp/my_fifo"
#define BUFFER_SIZE PIPE_BUF

int main(int argc, char *argv[])
{
  int res;
  int open_mode = 0;
  int n=0;
  char MYkey='A';
  open_mode= O_WRONLY | O_NONBLOCK;

  if (access(FIFO_NAME, F_OK) == -1) {
      res = mkfifo(FIFO_NAME, 0777);
      if (res != 0) {
          fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME);
          exit(EXIT_FAILURE);
      }
  }

  res = open(FIFO_NAME, open_mode);
  while(1)
  {
   n=write(res,&MYkey,BUFFER_SIZE);
   if(n>0)
    printf("write %c\n",MYkey);
   sleep(3);
   MYkey++;
  }
  exit(EXIT_SUCCESS);
}

執行結果：

[root@ecken02 fifo]# ./r &
[1] 16226
No Data.
[root@ecken02 fifo]# ./w
write A
A
No Data.
No Data.
write B
B
No Data.
No Data.
write C
C
No Data.

typedef for function pointer

#include <stdio.h>
typedef  void (*VPF) (int *, int *);
void Square(int *rX, int *rY);
void Swap(int *rX, int *rY);
void PrintVals(VPF,int , int );
 
int main()
{
  int valOne=2, valTwo=5;
  VPF pFunc;

  pFunc = Swap;
  PrintVals ( pFunc, valOne, valTwo);

  pFunc = Square;
  PrintVals ( pFunc, valOne, valTwo);

  return 0;
}
 
void PrintVals( VPF pFunc,int x, int y)
{
  printf("x:%d  y:%d\n",x,y);
  pFunc(&x,&y);
  printf("x:%d  y:%d\n",x,y);
  printf("\n");
}

void Square(int *rX, int *rY)
{
  (*rX) *= (*rX);
  (*rY) *= (*rY);
}

void Swap(int *rX, int *rY)
{
  int temp;
  temp = *rX;
  *rX = *rY;
  *rY = temp;
}

執行結果：

x:2  y:5
x:5  y:2

x:2  y:5
x:4  y:25