在c中使用strcmp比较字符串

Question

我的目标是让服务器在从客户端收到 "hello" 时打印 "it works"。 strcmp 功能对我不起作用。我被告知使用 f(strncasecmp(message,mess,5)) 代替，但是它仅在客户端使用 netcat 与“^c”断开连接时打印它才有效。一段时间以来，我一直在努力解决这个问题，但一无所获。在客户端，我现在只使用 netcat。如果您有任何问题，请在第一次投票时放轻松。

#include<stdio.h>
#include<string.h>  //strlen
#include<stdlib.h>  //strlen
#include<sys/socket.h>
#include<arpa/inet.h>   //inet_addr
#include<unistd.h>  //write

#include<pthread.h> //for threading , link with lpthread

void *connection_handler(void *);

int main(int argc , char *argv[])
{
    int socket_desc , new_socket , c , *new_sock;
    struct sockaddr_in server , client;
    char *message;

    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }

    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 9999 );

    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        puts("bind failed");
        return 1;
    }
    puts("bind done");

    //Listen
    listen(socket_desc , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while( (new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
        puts("Connection accepted");

        //Reply to the client
        message = "Hello Client , I have received your connection. And now I will assign a handler for you\n";
        write(new_socket , message , strlen(message));

        pthread_t sniffer_thread;
        new_sock = malloc(1);
        *new_sock = new_socket;

        if( pthread_create( &sniffer_thread , NULL ,  connection_handler , (void*) new_sock) < 0)
        {
            perror("could not create thread");
            return 1;
        }

        //Now join the thread , so that we dont terminate before the thread
        //pthread_join( sniffer_thread , NULL);
        puts("Handler assigned");
    }

    if (new_socket<0)
    {
        perror("accept failed");
        return 1;
    }

    return 0;
}
/*
 * This will handle connection for each client
 * */
void *connection_handler(void *socket_desc)
{
    //Get the socket descriptor
    int sock = *(int*)socket_desc;
    int read_size;
    char *message , client_message[2000];
    //char *contents;
    //contents = "hello";
    //strcpy(mess,contents);
    //Send some messages to the client
    message = "Greetings! I am your connection handler\n";
    write(sock , message , strlen(message));

    message = "Now type something and i shall repeat what you type \n";
    write(sock , message , strlen(message));

    //Receive a message from client
    while( (read_size = recv(sock , client_message , 2000 , 0)) > 0 )
    {
        write(sock , client_message , strlen(client_message));
        char mess[] = "hello";

Issue is here "if(strcmp(message, mess))"

        if(strcmp(message, mess)){
        printf("it works");
    }
    }
    if(read_size == 0)
    {
        puts("Client disconnected");
        fflush(stdout);
    }
    else if(read_size == -1)
    {
        perror("recv failed");
    }

    //Free the socket pointer
    free(socket_desc);

    return 0;
}

Answer 1

在你的条件下，你检查if(strcmp(message, mess))，如果message和mess不同，它将被执行 ，如 strcmp returns 0 仅当比较的字符串相等时。因此，您需要将此行更改为：

if(strcmp(message, mess) == 0)

以便在字符串相同的情况下执行 if 部分中的语句。

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