Reading Data from File into Array - C

Question

I'm doing a project on Kali Linux where I run the tool Ettercap that lists IP addresses on a network and saves them to a .txt. I then need to use these IP's on another tool nmap, so I wanted to write a C code that can save the IPs from IP.txt into an array. So far this is the closest working code:

#include <stdio.h>
#include <stdlib.h>

main(){

    FILE *ipList;
    ipList = fopen("IP.txt", "r");

    int ipArray[10];
    int i;

    if (ipList == NULL)
    {
        printf("Error\n");
        exit (0);
    }
    for (i = 0; i < 10; i++)
    {
        fscanf(ipList, "%d,", &ipArray[i] );

    }

    for (i = 0; i < 10; i++)
    {
           printf("nmap -A -T4 -F %d\n\n", ipArray[i]);
        }

    fclose(ipList);

    return 0;
}

The resulting output is just a bunch of random numbers. Any ideas? Does it matter that I'm using Kali? And my ipArray is set to 10; will it be a problem if I don't have 10 ip addresses?

The IP addresses are stored like this:

IP address : 10.0.0.1

IP address : 10.0.0.2

IP address : 10.0.0.3

IP address : 10.0.0.4

I've made progress. This is my current out put:

Here is my current code:

#include <stdio.h>

#include <stdlib.h>



main() {



FILE *ipList;
ipList = fopen("IP.txt","r");



char ip_addr[256];



while (fscanf(ipList, "%255s", ip_addr) == 1){

printf("nmap -A -T4 -F %s|n", ip_addr);

}



if (ipList == NULL){

printf("error\n");

exit (1);

}



fclose(ipList);

return 0;

}

So now my goal is to have the code ignore "IP address :" and if possible output it as a list.

You don't check the return value from fscanf() so you've no idea whether it thinks it was able to read an integer from the input. You'll never know whether the comma was matched or not, which probably doesn't matter. Your error message should be printed on standard error (stderr), not standard output. Your error exit should probably be 1 or EXIT_FAILURE rather than 0 which indicates success. The fact that you're using Kali Linux is almost certainly completely immaterial. Your code is completely standard C, except that you should have an explicit return type: int main(). — Jonathan Leffler
– Jonathan Leffler, Commented Apr 26, 2015 at 4:29
The only thing I can add on to @JonathanLeffler's remark is that you seem to be confusing %d (and int) for some non-existent format specifier (and type) that represents IP addresses, and you should probably use %s (corresponding to an array of char, rather than a pointer to int) to handle this input as strings, instead... char ip_addr[256]; while (fscanf(ipList, "%255s", ip_addr) == 1) { printf("nmap -A -T4 -F %s\n", ip_addr); } — autistic
– autistic, Commented Apr 26, 2015 at 4:38
@undefinedbehaviour: Good point. If the IP addresses are comma separated, though, that might need to be "%255[^,],". — Jonathan Leffler
– Jonathan Leffler, Commented Apr 26, 2015 at 4:40
Thanks for all this help, everyone. Actually, when the list of IP's is generated, its in the form of a list instead of side by side or separated by commas. — John
– John, Commented Apr 26, 2015 at 15:59
@JonathanLeffler A good point to raise along this tangential line is that "%255[^,]," introduces a different challenge with regards to failure modes. — autistic
– autistic, Commented Apr 27, 2015 at 0:05

Jonathan Leffler · Accepted Answer · 2015-04-27 00:12:51Z

1

Given that the input format is lines such as:

IP address : 10.0.0.1

then you need to read the address as a string, or as 4 separate small integers.

char *ip_address[16];

for (i = 0; i < 10; i++)
{
    if (fscanf(fp, "IP address : %15s", ip_address) != 1)
        …report format error…
    …code to convert dotted-decimal to IPv4 address…
}

or:

int ip[4];

for (i = 0; i < 10; i++)
{
    if (fscanf(fp, "IP address : %d.%d.%d.%d", &ip[0], &ip[1], &ip[2], &ip[3]) != 4)
        …report format error…
    for (j = 0; j < 4; j++)
    {
        if (ip[j] < 0 || ip[j] > 255)
            …report bogus value…
    }
    …convert dotted-decimal values into IPv4 address…
}

answered Apr 27, 2015 at 0:12

Jonathan Leffler

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