#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>         /* See NOTES */
#include <sys/socket.h>

#define BACKLOG 10

//./a.out ip port
int main(int argc,char *argv[])
{
    int sfd,cfd,ret;
    struct sockaddr_in svr_addr,cli_addr;
    char buffer[1024] = {0};
    ssize_t sbytes = 0,rbytes = 0;
    int length;
    int total_received;
    socklen_t len = sizeof(struct sockaddr_in);
    if (argc != 3){
        fprintf(stderr,"Usage : %s < ip > < port >.\n",argv[0]) ;
        exit(EXIT_FAILURE);
    }

    //1.创建套接字
    sfd = socket(AF_INET,SOCK_STREAM,0);
    if (sfd == -1){
        perror("[ERROR] Failed to socket.");
        exit(EXIT_FAILURE);
    }

    bzero(&svr_addr,sizeof(struct sockaddr_in));
    svr_addr.sin_family = AF_INET;
    svr_addr.sin_port = htons(atoi(argv[2]));
    svr_addr.sin_addr.s_addr = inet_addr(argv[1]);
    
    //2.绑定ip地址与端口号
    ret = bind(sfd,(const struct sockaddr *)&svr_addr,sizeof(struct sockaddr));
    if (ret == -1){
        perror("[ERROR] Failed to bind.");
        exit(EXIT_FAILURE);
    }
    //3.设置监听套接字为监听状态<span class="bd-box"><h-char class="bd bd-beg"><h-inner>，</h-inner></h-char></span>建立监听队列
    ret = listen(sfd,BACKLOG);
    if (ret == -1){
        perror("[ERROR] Failed to listen.");
        exit(EXIT_FAILURE);
    }

    //4.与客户端进行三次握手<span class="bd-box"><h-char class="bd bd-beg"><h-inner>，</h-inner></h-char></span>并建立连接,默认是阻塞
    cfd = accept(sfd,(struct sockaddr *)&cli_addr,&len);
    if (ret == -1){
        perror("[ERROR] Failed to accpet.");
        exit(EXIT_FAILURE);
    }

    printf("ip : %s port :%d\n",inet_ntoa(cli_addr.sin_addr),ntohs(cli_addr.sin_port));
    for(;;){
        length = 0;
        total_received = 0;
        //接收数据的长度
        rbytes = recv(cfd,&length,4,0);
        if (rbytes == -1){
            perror("[ERROR] Failed to recv.");
            exit(EXIT_FAILURE);
        }
        for(;;){

            rbytes = recv(cfd,buffer + total_received,length - total_received,0);
            if (rbytes == -1){
                perror("[ERROR] Failed to recv.");
                exit(EXIT_FAILURE);
            }else if (rbytes == 0){
                printf("The client has been shutdown.\n");
            }else if (rbytes > 0){
                total_received += rbytes;
                if (total_received == length)
                    break;
            }
        }
            printf("buffer : %s\n",buffer);
        sleep(1);
    }

    close(sfd);
<span class="bd-box"><h-char class="bd bd-beg"><h-inner>。</h-inner></h-char></span>
    return 0;
}  

int  atoi(const char *nptr)；
功能：把ntpr 所指向的整数字符串转换成整数。
参数：
    @  nptr    字符串
返回值：成功，返回转换后的整数
              失败，返回0
注意：若是只有+，-和整数字符能转换，其他字符返回0

uint32_t ntohs(uint32_t netlong);           [network to host short]
功能：把网络字节序转换为主机端口
参数：
@   netlong    网络字节序
返回值： 返回对应的主机端口

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>

void do_sig_usr(int sig)
{
    printf(" Receive %s \n",strsignal(sig));
}

int main(void)
{
    pid_t cpid;

    // 设置信号处理方式
    if(signal(SIGUSR1,do_sig_usr) == SIG_ERR){
        perror("[ERROR] signal(): ");
        exit(EXIT_FAILURE);
    }

    cpid = fork();

    if(cpid == -1){
        perror("fork(): ");
        exit(EXIT_FAILURE);
    }else if(cpid == 0){
        printf("Child Process < %d > start.\n",getpid());

        pause(); // 等待信号唤醒,这里需要信号到达之前进入睡眠状态

        exit(EXIT_SUCCESS);
    }else if(cpid > 0){

        sleep(1); // 延时 1s,让子进程先执行

        kill(cpid,SIGUSR1);// 给子进程发送 SIGUSR1 信号

        wait(NULL);// 等待子进程退出
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>
#include <string.h>

void do_sig_child(int sig)
{
    printf("Receive signal < %s >\n",strsignal(sig));
    wait(NULL);
}

int main(void)
{
    pid_t cpid;
    __sighandler_t sigret;

    sigret = signal(SIGCHLD,do_sig_child);
    if (sigret == SIG_ERR){
        perror("[ERROR] signal(): ");
        exit(EXIT_FAILURE);
    }   
    
    cpid = fork();
    if (cpid == -1){
        perror("[ERROR] fork(): ");
        exit(EXIT_FAILURE);
    }else if (cpid == 0){ 
        printf("Child process < %d > start.\n",getpid());
        sleep(2);
        exit(EXIT_SUCCESS);
    }else if (cpid > 0){ 
        while(1){
            /*nothing*/
        }
    }   
    return 0;
}

ar -rs file.a file.o