C chat program get an error Segmentation fault (core dumped)

Question

I am building a chat program between a client and a server in C language. Client will connect to server, sends to it a message. Then server will response that meesage.

If there is another client connects to server, the new connection will be created a new thread. So I use pthread.h to build a multi-threaded chat program in C. Please see the server.c and client.c code below to get more details.

server.c

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

#define PORT 7778

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

void *clientHandler(void*);

int main(){
    printf("INFO enter the main()\n");
    int sockfd, newsockfd, clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    int n, threadID;
    pthread_t interrupt;

    printf("INFO before calling socket()\n");
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
        printf("INFO after calling socket()\n");
    if(sockfd < 0)
        error("ERROR opening socket\n");

    printf("INFO before calling bzero()\n");
    bzero((char*) &serv_addr, sizeof(serv_addr));
    printf("INFO after calling socket()\n");

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons(PORT);
    printf("INFO after assigning Internet info\n");

    if(bind(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) < 0)    
    {
        error("ERROR on binding\n");
        return 0;
    }
    printf("INFO before calling listen()\n");

    listen(sockfd, 5);

    printf("INFO before entering While(1)\n");
    while(1)
    {
        int re;
        clilen = sizeof(cli_addr);
        printf("INFO before calling accept()\n");
        newsockfd = accept(sockfd, (struct sockaddr*)&cli_addr, &clilen);

        if(newsockfd < 0){
            error("ERROR on accepting\n");
            return 0;
        }
        printf("INFO before calling pthread_create()\n");
        re = pthread_create(&interrupt, NULL, clientHandler, NULL);
        if(re){
            printf("ERROR return code from the pthread_create() is %d\n", re);
        }       
    }
    printf("INFO before calling pthread_exit(NULL)\n");
    pthread_exit(NULL);
    return 0;
}

void *clientHandler(void *param){
    int n, newsockfd;
    newsockfd = *((int*)param);
    char buffer[256];
    bzero(buffer, 256);

    while(1){
        n = read(newsockfd, buffer, 255);

        if(n < 0){
            error("ERROR reading from socket\n");
            pthread_exit(NULL);
        }

        printf("Server received the message: %s", buffer);

        n = write(newsockfd, "Server got it\n", 18);

        if(n < 0){
            error("ERROR writing to socket\n");
            pthread_exit(NULL);
        }
    }
}

client.c

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

#define PORT 7778
#define HOSTNAME "127.0.0.1"

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

int main(){
    int sockfd, n;
    struct sockaddr_in serv_addr;
    struct hostent* server;
    //char *hostname = "127.0.0.1";

    char buffer[256];

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if(sockfd < 0)
        error("ERROR opening socket\n");

    server = gethostbyname(HOSTNAME);
    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(PORT);

    if(connect(sockfd, &serv_addr, sizeof(serv_addr)) < 0){
        error("ERROR connecting\n");
        return 0;
    }

    while(1)
    {    
        printf("Please enter the message: ");
        bzero(buffer, 256);
        fgets(buffer, 255, stdin);
        n=write(sockfd, buffer, strlen(buffer));

        if(n < 0){
            error("ERROR reading from socket\n");
            return 0;    
        }

        printf("[Server got it] %s\n", buffer);
    }

    return 0;
}

OK, I builded the *.c files successfully in Linux environment by using terminal.

I used this command line to build server.c

gcc server.c -o server.out -pthread

and use this one to build client.c

gcc client.c -o client.out

Then, I call server.out to run the server:

 ./server.out

and run client.out

./client.out 

BUT, at the time I run server.out, I got the error:

Segmentation fault (core dumped)

Guys, could you share with me your experiences about this. Is my code wrong in somewhere?

Answer 1

This line is passing NULL as the argument of the handler

 re = pthread_create(&interrupt, NULL, clientHandler, NULL);

It should be:

 re = pthread_create(&interrupt, NULL, clientHandler, &newsockfd);

as Sourav Ghosh comments.

Answer 2

You need to pass newsockt id to the new thread created.

so change

    re = pthread_create(&interrupt, NULL, clientHandler, (void*)&newsockfd);

I have added 3rd argument here

---

typecasting with (void*) will not give you one warning :)