child.cpp

一个演示多线程中共享文件操作符的例子。file是主线程

#include <cstdio>
#include <sys/stat.h>
#include <cerrno>
#include <fcntl.h>
#include <unistd.h>
#include <iostream>
#include <stdlib.h>

using namespace std;
int main(int argc, char *argv[])
{
   int fd;
   int n;


   const char*mark = "This is child process write.";

   char buf[50];


   if (argc != 2)
    {
      cout << "Usage: child <filename> " << endl;
      exit(0);
    }
   fd = atoi(argv[1]);  
   if(fd < 0)
    {
      perror("file descriptor error");
      exit(1);
    }
    n = write(fd,mark, strlen(mark));
   if (n == -1) 
    {
      perror("child write mark error");
      exit(1);
    }
   lseek(fd,0,SEEK_SET);
   
   n = read(fd, buf, sizeof(buf));
   if (n == -1) 
    {
     perror("read error");
     exit(1);
    }
   
   buf[n]='\0';
   cout << "Read the message is: "<< buf << endl;
   
close(fd);

   }