解决bind错误 bind: Address already in use

关于bind错误的处理：
bind: Address already in use

原因： 操作系统没有立即释放端口

解决一： 等待一段时间运行网络程序即可

解决二：通过setsockopt进行设置，关键代码如下。

        // 解决在close之后会有一个WAIT_TIME，导致bind失败的问题
    int val = 1;
    int ret = setsockopt(sfd,SOL_SOCKET,SO_REUSEADDR,(void *)&val,sizeof(int));
    if(ret == -1)
    {
        printf("setsockopt");
        exit(1);
    }     

举例：以多进程并发服务器为例

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

#include <sys/types.h>  
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>

#define PORT 7788

int init_tcp()
{
    // 1.创建套接字 - 设置协议
    int sfd = socket(AF_INET,SOCK_STREAM,0);
    if( -1 == sfd )
    {
        perror("socket");
        exit(-1);
    }
    //2. 解决在close之后会有一个WAIT_TIME，导致bind失败的问题
    int val = 1;
    int ret = setsockopt(sfd,SOL_SOCKET,SO_REUSEADDR,(void *)&val,sizeof(int));
    if(ret == -1)
    {
        printf("setsockopt");
        exit(1);
    }
    //3. 绑定IP和PORT
    struct sockaddr_in saddr;
    saddr.sin_family = AF_INET;
    saddr.sin_addr.s_addr = INADDR_ANY;
    saddr.sin_port = htons(PORT);
    ret = bind(sfd,(struct sockaddr *)&saddr,sizeof(saddr));
    if(ret == -1)
    {
        printf("bind");
        exit(1);
    }
    //4. 监听
    ret = listen(sfd,5);
    if(ret == -1)
    {
        printf("listen");
        exit(1);
    }
    printf("Server is ready ... \n");
    
    return sfd;
}

void deal_communication(int cfd)
{
    char buf[64] = {'\0'};
    while(1)
    {
        memset(buf,'\0',sizeof(buf));
        recv(cfd,buf,sizeof(buf),0);
        printf("client say:%s\n",buf);
        send(cfd,buf,strlen(buf),0);
        if(strncmp(buf,"quit",4) == 0)
        break;                
    }

    return ;
}


int main()
{
    //1. 初始化(创建套接字socket/地址复用+bind/listen)
    int sfd = init_tcp();
    //2. 并发处理客户端（accept / fork） 2-2通信
    while(1)
    {
        int cfd = accept(sfd,NULL,NULL);
        if(cfd == -1)
        {
            perror("accept");
            exit(1);
        }
        
        // fork - create a child process
        if(fork() == 0)
        {
            deal_communication(cfd);
            close(cfd);
            exit(0);
        }
        close(cfd);
        signal(SIGCHLD,SIG_DFL);
    }
    close(sfd);
    return 0;
}