Question

I am (trying to) write a server-side daemon in c, and it accepts connections from clients. I need a struct that keeps information on each open connection, so I have created an array of my defined struct, and I have it dynamically re-sizing with realloc.

The problem I have is creating the struct within the array. I keep getting this error:

test.c:41: error: conversion to non-scalar type requested

What am I doing wrong?

I spend most of my time in PHP, and am a noob with c. I realize that I am making some simple, beginner mistakes (in other words, feel free to make fun of me). If I am doing something stupid, please let me know. I’ve put my quality time in with google, but have not figured it out. I have reproduced the issue on smaller scale, as below:

here is my test.h:

typedef struct test_ test;

and here is my test.c:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "test.h"

//define the struct
struct test_ {
    int id;
    char *ip;
    int user;
    char *str;
};

//yes, the list needs to be global
test *test_list;


//
// add an item to the global list
//
int add(int id, char *ip, int size)
{
    //
    // increment size
    if(id>size) {
        size = id;
        //try to expand the list
        test *tmp = realloc(test_list,size);
        if(tmp) {
            //it worked; copy list back
            test_list = tmp;
        } else {
            //out of memory
            printf("could now expand list\n");
            exit(1);
        }
    }
    //
    // HERE IS THE TROUBLE CODE::
    test_list[id] = (struct test)malloc(sizeof(test)+(sizeof(int)*5)+strlen(ip)+1);
    test_list[id].id = id;
    test_list[id].ip = malloc(strlen(ip));
        strcpy(test_list[id].ip,ip);
    test_list[id].user = 0;
    test_list[id].str = NULL;
}

//
// main
//
int main(void)
{
    //initialize
    int size = 1;
    test_list = malloc(size*sizeof(test));
    //add 10 dummy items
    int i;
    for(i=0; i<10; i++) {
        size = add(i, "sample-ip-addr", size);
    }
    //that's it!
    return 0;
}

Answer 1

Try changing

test *tmp = realloc(test_list,size);

to

test *tmp = realloc(test_list,size*sizeof(test));

then delete

test_list[id] = (struct test)malloc(sizeof(test)+(sizeof(int)*5)+strlen(ip)+1);

When you allocate for test_list, there’s already space for each member of the struct allocated, so you don’t need to do it again. You just have to allocate for any pointers within the struct