如何从/write读取到匿名共享映射? [英] How to read from /write to anonymous shared mapping?

问题描述

尝试使用子进程将消息写入匿名共享内存，请终止该消息.然后让家长阅读该消息.我已经看到了映射输入&的示例.使用通过read& write通话.但是不知道如何正确地解决这个问题.

Attempting to write a message to anonymous shared memory with a child process, terminate it. Then have the message read by the parent. I have seen examples for mapping input & output files using file descriptors obtained through read & write calls. But do not know how to approach this correctly.

int main(void) {
  char *shared; 
  int status;
  pid_t child;

  shared = mmap(0, sizeof(int) , PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);

  if (shared == MAP_FAILED) {
    perror("mmap");
    return 1;
  }

  child = fork();

  if ( child == -1 ) {
    perror("fork");
    return 1;
  } else if (child == 0) {
    sprintf(shared, "foo");

  } else {
    printf("%s", shared);
    wait(&status);
  }

  if (munmap (shared, sizeof(int)) == -1) {
      perror("munmap");
      return 1;
  }

  return 0;    
}

推荐答案

如果您的唯一目标是在子进程和父进程之间进行读/写，则使用管道是一种更简单的方法.看起来像这样:

If your only goal is to read / write between a child process and a parent process, using pipes is a much easier method of doing so. It would look something like this:

    int fd[2]; 
    pipe(fd);

    if((child= fork()) == -1)
    {
            perror("fork");
            exit(1);
    }

    if(child == 0)
    {
            // close read side
            close(fd[0]);

            // write to pipe
            write(fd[1], msg, (strlen(msg));
    }
    else
    {
            //close write side
            close(fd[1]);

            //read what the child wrote. 
            nbytes = read(fd[0], buff, sizeof(buff));
    }

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