Examples on hooking the standard C socket library. Code for blog post https://fishi.devtail.io/weblog/2015/01/25/intercepting-hooking-function-calls-shared-c-libraries/

simple_client.c

/*
* A simple client that opens a socket.
*/

#include <stdio.h>
#include <sys/socket.h>
    
int main(int argc, char *argv[])
{
    int sockfd;
    
    // Create socket and check for error
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        perror("Error : Could not create socket\n");
        return 1;
    }
    else
    {
        printf("Socket successfully created\n");
    }
    
    return 0;
}

socket_hook.c

/*
* A simple socket hook which calls the original socket library.
*/

#define _GNU_SOURCE
#include <stdio.h>
#include <sys/socket.h>
#include <dlfcn.h>
    
int (*o_socket)(int,int,int);
    
int socket(int domain, int type, int protocol)
{
    // find the next occurrence of the socket() function
    o_socket = dlsym(RTLD_NEXT, "socket");
    
    if(o_socket == NULL)
    {
        printf("Could not find next socket() function occurrence");
        return -1;
    }
    
    printf("socket() call intercepted\n");
    
    // return the result of the call to the original C socket() function
    return o_socket(domain,type,protocol);
}

socket_hook_trivial.c

/*
* A trivial socket hook.
*/

#include <stdio.h>
    
int socket(int domain, int type, int protocol)
{
    printf("socket() call intercepted");
    return -1;
}