c - C 中带有通过 FIFO 管道的指针的结构

Question

我正在尝试使用一台服务器和一个客户端设置一个 FIFO 管道。

客户端.c

#include<stdio.h> 
#include<fcntl.h>
#include<stdlib.h>
#include<string.h>

typedef struct buffer {
     int pid;
     char *buffer;
 } my_buffer;

/*
void removefifo() {
unlink("fifo_server");
unlink("fifo_client");
}
*/

main(int argc, char *argv[]) {
    if (argc != 2) {
    fprintf(stderr, "usa: %s text \n", argv[0]);
    return EXIT_FAILURE;
    }

 FILE *file1;
 int fifo_server,fifo_client;
 char *buf_in;
 buf_in = malloc(20*sizeof(char));

 //send PID and content
 my_buffer * buf_out;
 buf_out = (my_buffer *)malloc(sizeof(my_buffer));
 buf_out->pid = getpid();
 buf_out->buffer = (char *) calloc(20,sizeof(char));
 strcpy(buf_out->buffer,argv[1]);

 fifo_server=open("fifo_server",O_RDWR);
 if(fifo_server < 0) {
  printf("Error in opening file");
  exit(-1);
  }

 printf("buffer has PID %d and content %s \n",buf_out->pid,buf_out->buffer);


 write(fifo_server,buf_out,sizeof(struct buffer));

 fifo_client=open("fifo_client",O_RDWR);

 if(fifo_client < 0) {
  printf("Error in opening file");
  exit(-1);
  }


 read(fifo_client,buf_in,10*sizeof(char));
 printf("\n * Reply from server: %s * \n",buf_in);
 close(fifo_server);
 close(fifo_client);

}

服务器.c

#include<stdio.h> 
#include<fcntl.h>
#include<stdlib.h>
#include<string.h>
#define FIFO_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) //0666

typedef struct buffer {
     int pid;
     char *buffer;
 } my_buffer;




int main()
{
int fifo_server,fifo_client;
char *buf_out;
int i;

int file1,file2;

my_buffer * buf_in;
buf_in = (my_buffer *)malloc(sizeof(my_buffer));
buf_in->buffer = (char *) calloc(20,sizeof(char));
buf_out = malloc(20*sizeof(char));

//create fifo-server with p-flag
file1 = mkfifo("fifo_server",FIFO_MODE); 
if(file1<0) {
 printf("FIFO_SERVER already exists \n");
 }

fifo_server = open("fifo_server",O_RDWR);
if(fifo_server<1) {
 printf("Error opening file");
 }
read(fifo_server,buf_in,sizeof(struct buffer)); //read PID and content
if(fifo_server<1) {
 printf("Error opening file");
 }

printf("pid %d \n",buf_in->pid);
printf("content %s \n",buf_in->buffer);

//write
strcpy(buf_out,buf_in->buffer);
for (i = 0; buf_in->buffer[i] != '\0'; i++) {
    buf_out[i] = toupper(buf_in->buffer[i]);
}

//create fifo-client with p-flag
file2 = mkfifo("fifo_client",FIFO_MODE); 
if(file2<0) {
 printf("FIFO_CLIENT already exists \n");
 }


fifo_client = open("fifo_client",O_RDWR);
write(fifo_client,buf_out,10*sizeof(char)); 
printf("\n Data sent to client \n");


close(fifo_server);
close(fifo_client);

}

我首先启动服务器，然后启动客户端。特别是，当我使用

运行客户端时

./client "the fox"
buffer has PID 14491 and content the fox 

服务器正确显示 PID，但在打印 buf_in->buffer 时崩溃。

./server 
pid 14491 
Errore di segmentazione

请征求您的建议。

Answer 1

您的struct buffer在其成员中包含一个指针。这很好，但您需要认识到，无论指向什么，如果有的话，都不是 struct 的一部分，并且指针本身充其量是 em> 在管道的另一端无效。您有两个主要选择:

1. 为您的struct提供一个数组成员而不是指针成员:

   typedef struct buffer {
       int pid;
       char buffer[20];
   } my_buffer;
   

2. 在编写数据时要更加小心。例如:

   unsigned buf_size = strlen(buf_out.buffer);
   write(fifo_client, &buf_out.pid, sizeof(buf_out.pid));
   write(fifo_client, &buf_size, sizeof(buf_size));
   write(fifo_client, buf_out.buffer, buf_size);
   

自然，后者必须搭配相应的读取机制。