Question

I am doing C sockets for the first time and I am running into a small error with my code. As I compile it works correctly and compiles fine it just throws some errors and I want to know how to fix them.

Here is the code:

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

#define PORTNUM 2343

int main(int argc, char *argv[])
{
    char msg[] = "Hello World !\n";

    struct sockaddr_in dest; /* socket info about the machine connecting to us */
    struct sockaddr_in serv; /* socket info about our server */
    int mysocket;            /* socket used to listen for incoming connections */
    int socksize = sizeof(struct sockaddr_in);

    memset(&serv, 0, sizeof(serv));    /* zero the struct before filling the fields */
    serv.sin_family = AF_INET;         /* set the type of connection to TCP/IP */
    serv.sin_addr.s_addr = INADDR_ANY; /* set our address to any interface */
    serv.sin_port = htons(PORTNUM);    /* set the server port number */    

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    /* bind serv information to mysocket */
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));

    /* start listening, allowing a queue of up to 1 pending connection */
    listen(mysocket, 1);
    int consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);

    while(consocket)
    {
        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(dest.sin_addr));
        send(consocket, msg, strlen(msg), 0); 
        consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);
    }

    close(consocket);
    close(mysocket);
    return EXIT_SUCCESS;
}

I got this from a website as an simple example.

Here is the compiler error:

server.c: In function ‘main’:
server.c:33:46: warning: pointer targets in passing argument 3 of ‘accept’ differ in signedness [-Wpointer-sign]
/usr/include/i386-linux-gnu/sys/socket.h:214:12: note: expected ‘socklen_t * __restrict__’ but argument is of type ‘int *’
server.c:39:46: warning: pointer targets in passing argument 3 of ‘accept’ differ in signedness [-Wpointer-sign]
/usr/include/i386-linux-gnu/sys/socket.h:214:12: note: expected ‘socklen_t * __restrict__’ but argument is of type ‘int *’

Thanks for the help! 🙂

Answer 1

C and C++ headers often define types for portability and to enforce certain relationships.

As you have seen, a lot of code will compile and run with warnings.

However, they are warnings for a reason.

Otherwise, one day you might be in some corner case where size and signedness matter, and you won’t know why it doesn’t work. Always try to follow the conventions of the library you are using.

To fix your current warnings, you need to declare socksize as socklen_t.