讀/寫：非法搜索 - 客戶端 - 服務器C ++

Question

我發現stackoverflow客戶端 - 服務器代碼（使用命名管道），我修改它讓客戶端在while循環中發送消息。 雖然我從服務器收到消息，但我在讀/寫時得到“非法搜索”，我不確定這是否是一個嚴重的錯誤，如果這里真的很糟糕？

server.cpp

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

int main()
{
   int client_to_server;
   char *myfifo = "/tmp/client_to_server_fifo";

   int server_to_client;
   char *myfifo2 = "/tmp/server_to_client_fifo";

   char buf[BUFSIZ];

   /* create the FIFO (named pipe) */
   mkfifo(myfifo, 0666);
   mkfifo(myfifo2, 0666);

   /* open, read, and display the message from the FIFO */
   client_to_server = open(myfifo, O_RDONLY);
   server_to_client = open(myfifo2, O_WRONLY);

   printf("Server ON.\n");

   while (1)
   {
      read(client_to_server, buf, BUFSIZ);

      if (strcmp("exit",buf)==0)
      {
         printf("Server OFF.\n");
         break;
      }

      else if (strcmp("",buf)!=0)
      {
         printf("Received: %s\n", buf);
         printf("Sending back...\n");
         write(server_to_client,buf,BUFSIZ);
      }

      /* clean buf from any data */
      memset(buf, 0, sizeof(buf));
   }

   close(client_to_server);
   close(server_to_client);

   unlink(myfifo);
   unlink(myfifo2);
   return 0;
}

client.cpp

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

int main()
{
   int client_to_server;
   char *myfifo = "/tmp/client_to_server_fifo";

   int server_to_client;
   char *myfifo2 = "/tmp/server_to_client_fifo";

   char str[BUFSIZ];


   //printf("Input message to serwer: ");
   //scanf("%s", str);


   /* write str to the FIFO */
   client_to_server = open(myfifo, O_WRONLY);
   server_to_client = open(myfifo2, O_RDONLY);

while(true)
{

   printf("> "); 
   scanf("%s", str);
   write(client_to_server, str, sizeof(str));

   perror("Write:"); //Very crude error check

   read(server_to_client,str,sizeof(str));

   perror("Read:"); // Very crude error check

   printf("From  server: %s\n",str);
}
   close(client_to_server);
   close(server_to_client);

   /* remove the FIFO */

   return 0;
}

示例輸出：

客戶 ：

> hello, server!
Write:: Success
Read:: Illegal seek
From  server: hello,
Write:: Illegal seek
Read:: Illegal seek
> From  server: server!
> its client here!
Write:: Illegal seek
Read:: Illegal seek
From  server: its
Write:: Illegal seek
Read:: Illegal seek
> From  server: client
Write:: Illegal seek
Read:: Illegal seek
> From  server: here!
> > hello, server!
// and so on ...

服務器 ：

Server ON.
Received: hello,
Sending back...
Received: server!
Sending back...
Received: its
Sending back...
Received: client
Sending back...
Received: here!
Sending back...
Received: >
Sending back...
Received: hello,
Sending back...
Received: server!
Sending back...
Received: Write::
Sending back...
Received: Success
Sending back...
Received: Read::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: From
Sending back...
Received: server:
Sending back...
Received: hello,
Sending back...
Received: Write::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: Read::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: >
Sending back...
Received: From
Sending back...
Received: server:
Sending back...
Received: server!
Sending back...
Received: >
Sending back...
Received: its
Sending back...
Received: client
Sending back...
Received: here!
Sending back...
Received: Write::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: Read::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: From
Sending back...
Received: server:
Sending back...
Received: its
Sending back...
Received: Write::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: Read::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: >
Sending back...
Received: From
Sending back...
Received: server:
Sending back...
Received: client
Sending back...
Received: Write::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: Read::
Sending back...
Received: Illegal
Sending back...
Received: seek
Sending back...
Received: >
Sending back...
Received: From
Sending back...
Received: server:
Sending back...
Received: here!
Sending back...
Received: >
Sending back...

Answer 1

如果沒有錯誤，請不要調用perror 。

您需要在調用perror之前檢查先前的函數調用是否失敗，否則在沒有錯誤發生時您將收到無意義的錯誤消息。 如果它們沒有失敗，則不需要函數（通常）將errno為任何特定的東西。