c - 程序运行不符合我的预期

Question

我想知道为什么我的程序运行但没有按我预期的那样运行。我正在使用 fork() 创建客户端-服务器，但结果是:server2: success，但不是我想要的 listening。我用 gcc -o server2 server2.c

编译它

这是服务器端:

#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/wait.h> // trap the child exits and prevent zombies
#include <signal.h> // trap the child exits and prevent zombies
#include <stdlib.h>

// signal handler calls waitpid()
void sigchld_handler(int signo)
{
    while(waitpid(-1, NULL, WNOHANG) > 0);
}

// declares variabel
int main(int argc, char *argv[])
{
    struct sockaddr_in sAddr;
    int listensock;
    int newsock;
    char buffer[25];
    int result;
    int nread;
    int pid;
    int val;

// create socket that will accept connection
    listensock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

// set our SO_REUSEADDR option
    val = 1;
    result = setsockopt(listensock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
    if(result < 0){
      perror("server1 multiplexing");
      return 0;
    }

// bind to local port and all addresses associated with the machine
    sAddr.sin_family = AF_INET;
    sAddr.sin_port = htons(1972);
    sAddr.sin_addr.s_addr = INADDR_ANY;
    result = bind(listensock, (struct sockaddr *) &sAddr, sizeof(sAddr));
    if(result < 0){
      perror("server2");
      return 0;
    }

// put the socket into listening mode for incoming connections
    result = listen(listensock, 5);
    if(result < 5){
      perror("server2");
      return 0;
    }

// before start looping, we install our signal handler
    signal(SIGCHLD, sigchld_handler);

// call accept() to block waiting for connection request from clients, after accept returns call fork() to create a new process
    while(1){
      newsock = accept(listensock, NULL, NULL);
      if((pid = fork()) == 0){

// close listening socket, read char from client vice versa, close the socket and exit child process
        printf("child process %i created.\n", getpid());
        close(listensock);

      nread = recv(newsock, buffer, 25, 0);
      buffer[nread] = '\0';
      printf("%s\n", buffer);
      send(newsock, buffer, nread, 0);
      close(newsock);
      printf("child process %i finished.\n", getpid());
      exit(0);
      }else{
      printf("child process error");    
      }

// parents process close
    close(newsock);
    }
}

这是客户端:

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

void child_func(int childnum);

// main function
int main(int argc, char *argv[])
{
    int nchildren = 1;
    int pid;
    int x;

    if (argc > 1){
    nchildren = atoi(argv[1]);
    }

    for (x=0; x < nchildren; x++){
      if((pid = fork() == 0)){
        child_func(x+1);
        exit(0);
      } 
    }
    wait(NULL);
    return 0;
}
    void child_func(int childnum){
    int sock;
    struct sockaddr_in sAddr;
    char buffer[25];

    // create client socket and bind it to local pprt
    memset((void *) &sAddr, 0, sizeof(struct sockaddr_in));
    sAddr.sin_family = AF_INET;
    sAddr.sin_addr.s_addr = INADDR_ANY;
    sAddr.sin_port = 0;

    sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    bind(sock, (const struct sockaddr *) &sAddr, sizeof(sAddr));
    // Attempt to connect to whichever server is running on the local machine
    sAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    sAddr.sin_port = htons(1972);

    if (connect(sock, (const struct sockaddr *) &sAddr, sizeof(sAddr)) != 0){
    perror("client");   
    return;
    }
    // send some character to the server and insert sleep() function
    snprintf(buffer, 128, "data from client #%i.", childnum);
    sleep(1);
    printf("child #%i sent %zu chars\n", childnum, send(sock, buffer, strlen(buffer), 0));
    sleep(1);
    printf("child #%i received %zu chars\n", childnum, recv(sock, buffer, 25, 0));
    //close connection
    sleep(1);
    close(sock);

}

Answer 1

我想我知道你为什么得到输出

server2: success

然后为什么退出。

这是因为您如何检查 listen 中的错误功能。出错时返回 -1成功后返回 0 .就像大多数其他系统调用一样。它不会在成功时返回您传递给它的数字。

所以 listen 调用成功并返回 0 , 但随后您检查 result < 5零确实小于五，因此您打印“错误”并退出程序。