c - 想要在服务器上接收客户端发送的消息包......用C语言

Question

    /* A simple server in the internet domain using TCP
   The port number is passed as an argument */
     #include <stdio.h>
     #include <stdlib.h>
     #include <string.h>
     #include <unistd.h>
     #include <sys/types.h> 
     #include <sys/socket.h>
     #include <netinet/in.h>



void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
     int sockfd, newsockfd, portno;
     socklen_t clilen;
     char buffer[256];
     struct sockaddr_in serv_addr, cli_addr;
     int n;
     if (argc < 2) {
         fprintf(stderr,"ERROR, no port provided\n");
         exit(1);
     }
     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0) 
        error("ERROR opening socket");
     bzero((char *) &serv_addr, sizeof(serv_addr));
     portno = atoi(argv[1]);
     serv_addr.sin_family = AF_INET;
     serv_addr.sin_addr.s_addr = INADDR_ANY;
     serv_addr.sin_port = htons(portno);
     if (bind(sockfd, (struct sockaddr *) &serv_addr,
              sizeof(serv_addr)) < 0) 
              error("ERROR on binding");
     listen(sockfd,5);
     clilen = sizeof(cli_addr);
     newsockfd = accept(sockfd, 
                 (struct sockaddr *) &cli_addr, 
                 &clilen);
     if (newsockfd < 0) 
          error("ERROR on accept");
     bzero(buffer,256);
     n = read(newsockfd,buffer,255);
     if (n < 0) error("ERROR reading from socket");
     printf("Here is the message: %s\n",buffer);
     n = write(newsockfd,"I got your message",18);
     if (n < 0) error("ERROR writing to socket");
     close(newsockfd);
     close(sockfd);
     return 0; 
}










======>>>now client code


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

void error(const char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }
    portno = atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, 
         (char *)&serv_addr.sin_addr.s_addr,
         server->h_length);
    serv_addr.sin_port = htons(portno);
    if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0) 
        error("ERROR connecting");
    printf("Please enter the message: ");
    bzero(buffer,256);
    fgets(buffer,255,stdin);
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);
    close(sockfd);
    return 0;
}

//我是新手，所以请忽略愚蠢的提问方式

这段代码是通过n/w获取简单的字符串。现在我想获得要发送和接收的预定义类型标准消息，为此我必须定义一个结构，

现在我的问题是如何用 C 语言发送并获取 n/w 结构。请帮助我。 强文字

Answer 1

好吧，看一下编写原型(prototype):

ssize_t write(int fd, const void *buf, size_t count);

第二个参数是一个通用的 void 指针，因此您可以发送任何您想要的内容。在那里输入要传输的结构的地址及其大小。

还有要考虑的字节序(小字节序与大字节序)。如果正在通信的机器具有不同的字节顺序，则此方法不起作用。看看那些conversion functions像htons，ntohs，...

如果您要发送的数据结构使用机器字节顺序存储原始类型，则发送整个结构不起作用。您应该按网络顺序存储每个值，例如:

struct foo{
   uint32_t a;
   uint16_t b;
}foo; 

foo f;
f.a = htonl(10);
f.b = htons(5);

write(fd, (void *)&f, sizeof(foo));