CODEWITHSUNDEEP
cunix
Charlotte45
Charlotte45

Reputation: 143

htons and ntohs not working? C UNIX networking

I'm new to network programming in C and I started off by trying to send an array read from the keyboard to the server. The problem is that whenever I read the length of my array from the keyboard, it will add 2/3 and just not do anything right anymore. For example:

Length or array that I give: 2 The client will read from the keyboard 4 or 5 elements and if itry to print them afterwards, they don't have the value that I gave them. They get some totally different numbers.

This is how my client looks like:

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>

int main(int argc, char* argv[]) {
    int sockfd;
    struct sockaddr_in server;
    /*char msg[1000], serv_reply[2000];*/


    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("Error in creating the stupid sock client ");
        exit(errno);
    }

    puts("Socket created in client ");
    memset(&server, 0, sizeof(server));
    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    server.sin_family = AF_INET;
    server.sin_port = htons(9255);

    if ( connect(sockfd, (struct sockaddr*)&server, sizeof(server)) < 0) {
        perror("Connection failed ");
        exit(errno);
    }

    puts("Yey! Connected");

    printf("Let's try \n" );
    printf("Nr of elem = ");
    **int a;
    scanf("%d", &a);
    a = htons(a);
    if ( send(sockfd, &a, sizeof(a), 0 ) < 0 ) {
        perror("CLient sent error");
        exit(errno);
    }
    int i, elem;
    for( i =0; i<a; i++) {
        printf("Enter a number: ");
        scanf("%d", &elem);
        elem = htons(elem);
        printf("%d", elem);
        if ( send(sockfd, &elem, sizeof(elem), 0) < 0) {
            perror("Couldn't send the damn element ");
            exit(errno);
        }
    }**
    int somth;
    recv(sockfd, &somth, sizeof(somth), 0);
    somth = ntohs(somth);
    printf("WE GOT IT %d ", somth);
    close(sockfd);
}

Here is my server:

#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MY_PORT 9999
#define MAXBUF 1024

int main (int argc, char* argv[]) {
    int sockfd;
struct sockaddr_in server, client;
int c, l;

if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    perror("Error creating the stupid socket ");
    exit(errno);
}

memset(&server, 0, sizeof(server));
server.sin_port = htons(9255);
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;

if ( bind(sockfd, (struct sockaddr *) &server, sizeof(server)) < 0) {
    perror("Error in socket binding ");
    exit(errno);
}

if ( listen (sockfd, 20) < 0) {
    perror("Erro listening to the dumb sock ");
    exit(errno);
}
printf("WE'RE ON!! " );
l = sizeof(client);
memset(&client, 0, l);

while(1) {
    int a;


    c = accept(sockfd, (struct sockaddr *) &client, &l);
        if (c == -1) {
            perror("Error accepting connection");
            continue;
        } else {     
            printf("Cool, we have a new client! \n");
        }


    if (recv( c, &a, sizeof(a), MSG_WAITALL) < 0) {
        perror("Error reading in server ");
        exit(errno);
    }

    a = ntohs(a);

    int i, elem,sum;
    for ( i = 0; i<a; i++) {
        if ( recv(c, &elem, sizeof(elem), MSG_WAITALL)< 0) {
            perror("Error reading elems ");
            exit(errno);
        }
        elem = ntohs(elem);
        sum = sum + elem;
    }
    sum= ntohs(sum);

    if ( send(c, &sum, sizeof(sum), 0) < 0) {
        perror("Error sending to client ");
        exit(errno);
    }

    close(c);
}
}

I tried switching the htons to ntohs and the inverse and the same problem. Any idea what's wrong?

Upvotes: 1

Views: 1850

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409364

One major problem is that you loose the original a you enter in the client, so when you later use it in the loop condition it might not be what you expect.

Another major problem is that the s in e.g. htons stands for short, and on modern PC systems short is usually 16 bits while int is 32 bits.

Try using htonl and ntohl instead!

Upvotes: 1

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