c - C 中的静态变量

Question

我有这个程序，它是具有 tcp 协议(protocol)的服务器的一部分，它从客户端获取一个数字并将其用于另一个函数。 另外，我有一个 static int 类型变量，我想在服务器每次从客户端收到消息时对其进行计数，但每次它都不会保留其值； 变量是counter 你们能告诉我为什么会发生这种情况吗？

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <signal.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// used port 
#define PORT 1114

// error code 
extern int errno;

static int counter;

int main ()
{
  struct sockaddr_in server;  // structure used by server
  struct sockaddr_in from;  
  char message[100];         //message received from client
  int socketDescriptor;     //socket descriptor 


  //creating socket
  if ((socketDescriptor = socket (AF_INET, SOCK_STREAM, 0)) == -1)
  {
    perror ("[server]Error at socket\n");
    return errno;
  }

  //preparing data structures
  bzero (&server, sizeof (server));
  bzero (&from, sizeof (from));

  //filling structures
  server.sin_family = AF_INET;  

  server.sin_addr.s_addr = htonl (INADDR_ANY);

  server.sin_port = htons (PORT);

  //attach socket to descriptor
  if (bind (socketDescriptor, (struct sockaddr *) &server, sizeof (struct sockaddr)) == -1)
  {
    perror ("[server]Error at bind\n");
    return errno;
  }

  //server is listening
  if (listen (socketDescriptor, 2) == -1)
  {
    perror ("[server]Error at listen\n");
    return errno;
  }

  /serving concurrent the clients

  while (1)
  {
    int client;
    int length = sizeof (from);

    printf ("[server]Waiting at port %d...\n",PORT);
    fflush (stdout);

    //accepting client

    client = accept (socketDescriptor, (struct sockaddr *) &from, &length);
    counter ++;
    switch(fork())
    {
      case -1: 
        perror("fork err\n");
        exit(2);
    case 0:
      //error if failed connection
      if (client < 0)
      {
        perror ("[server]Error at accept\n");
        continue;
      }
      //conenction established
      bzero (message, 100);
      printf ("[server]Waiting for message...\n");
      fflush (stdout);

      //reading message
      if (read (client, message, 100) <= 0)
      {
        perror ("[server]Error at read\n");
        close (client); //closing connection
        continue;   //keep listening
      }

      printf ("[server]Message was received%s\n", message);
      //this is where I want to increment counter, when I want to  verify     message

      int number;
      number = atoi(message);//convert char to int

      printf("The number is: %d\n", number);//print number

      printf("The counter is : %d\n", counter);

      fflush(stdout);

  exit(2);
    }
  close (client);
  }      /* while */
}       /* main */

Answer 1

只需将 counter++ 移动到父进程即可。当子进程启动时，它会获取 counter 的副本，并且您修改的副本不会影响其在父进程中的副本(实际上是原始副本)。如果您在父进程中更新它，您将实现您想要的。

int main(int argc, char ** argv)
{
    int number;
    int listenfd, connfd, n;
    pid_t childpid;
    socklen_t clilen;
    char message[MAXLINE], answer[MAXLINE];
    struct sockaddr_in clientaddr, serveraddr;
    int counter;

    counter = 0;
    // create socket
    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        perror("ERROR at creating socket\n");
        exit(2);
    }

    // preparation of socket address
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
    serveraddr.sin_port = htons(PORT);

    // bind the socket
    bind(listenfd, (struct sockaddr *) &serveraddr, sizeof(serveraddr));

    // listen to the socket
    listen(listenfd, LIMIT);

    printf("Server running, waiting for connections at port : %d\n", PORT);

    while (1)
    {
        clilen = sizeof(clientaddr);
        // accept a connection
        connfd = accept(listenfd, (struct sockaddr *) &clientaddr, &clilen);
        printf("Recieved guest\n");
        switch (fork())
        {
        case -1:
            perror("fork err\n");
            exit(2);
        case 0:
            /* eroare la acceptarea conexiunii de la un client */
            if (connfd < 0)
            {
                perror("[server]Eroare la accept().\n");
                continue;
            }

            /* s-a realizat conexiunea, se astepta mesajul */
            bzero(message, 100);
            printf("[server]Asteptam mesajul...\n");
            fflush(stdout);

            /* citirea mesajului */
            if (read(connfd, message, 100) <= 0)
            {
                perror("[server]Eroare la read() de la client.\n");
                close(connfd); /* inchidem conexiunea cu clientul */

                continue;   /* continuam sa ascultam */
            }
            printf ("[server]Message was received...%s\n", message);
            fflush(stdout);

            number = atoi(message);

            printf("The number is: %d\n", number);
            printf ("%d\n", counter + 1);
            _exit(0); // The child should not create further grand children
        default:
            counter++;
            break;
        }//switch
    }//for
    close(connfd);
}//main