Array and segmentation fault

[Mz3g]

Hi guys,
When I run this code, I got segmentation fault and i can't figure out where the mistake is? I'd really appreciate any help. thanks

#include <fstream>
#include <iostream>
#include <string>
#include <sstream>

using namespace std;
int main ()
{
    ifstream file, dest;
    file.open ("arp.txt");
    if (!file)
    {
        cout << "Unable to open file"; // if file doesn't exist
        exit(1);
    }
	
	int size = 16;
	string v, ip[15], mac[15], IPs, IPd; 
	
	for (int k = 0; k < size; k++)  // reading the first file
	{
		file >> v >> v >> v >> ip[k] >> mac[k]; // v reads all the things before the IP
	}
	
	file.close ();
	
	dest.open ("dest.txt");
    if (!file)
    {
        cout << "Unable to open file"; // if file doesn't exist
        exit(1);
    }
	
	int s, d, z;
	dest >> v >> v >> v >> s; // here s will read an integer number from 0 - 15
	IPs = ip[s];
	dest >> v >> v >> IPd; // IPd will have an IP address that similar to one of the ip[k]
	
	for (int m = 0; m < size; m++)  
	{
		if (IPd == ip[m])
		{
			d = m; 
		}
	}

[Nick Evan]

This loop:

for (int k = 0; k < size; k++)

will insert values in ip[k], where k = a number between 0-15.
However you declared "ip" as an array with only 15 elements: string v, ip[15]... which means you can only use index 0-14. So when you try to write to index 15 --> boom! Segmentation fault.

[Mz3g]

Thank you very much Nick. I just got one more question,
Can I open 16 files and write to them in a simple way rather than this way? and I'll write to them more than one time during my program.

ofstream f0, f1, f2, f3 ,f4 ,f5 ,f6 ,f7;
ofstream f8 ,f9, f10, f11, f12 ,f13, f14 ,f15;
f0.open ("N0.txt"), f1.open ("N1.txt"), f2.open ("N2.txt");
f3.open ("N3.txt"), f4.open ("N4.txt"), f5.open ("N5.txt");
f6.open ("N6.txt"), f7.open ("N7.txt"),f8.open ("N8.txt");
f9.open ("N9.txt"), f10.open ("N10.txt"), f11.open ("N11.txt");
f12.open ("N12.txt"), f13.open ("N13.txt"), f14.open("N14.txt");
f15.open ("N15.txt");

Thanks in advance!

[CMPITG]

Why don't you use arrays, it would be like this

ofstream f[16];
char buffer[255];
for (int i = 0; i < 16; i++)
{
    snprintf(buffer, sizeof(buffer) - 1, "N%d.txt", i);
    f[i].open(buffer);
}

/* Then do what you want here,
 * use f[i] instead of f_i as your old code. */

You can use sprintf() instead of snprintf() but that function is really unsafe because the compiler does not perform the bound checking.

[Mz3g]

thanks a lot but i'm writing my codes in c++ so I did it like this:

int size = 16;
        ofstream f[16];
	stringstream ssFileName;
	for (int k = 0; k < size; k++) // prepare 16 files to write to them
	{
		ssFileName << "N" << k << ".txt";
		f[k].open (ssFileName.str().c_str());
	}	
        // some other codes and then
        f[d] << "I received a packet from Node " << s << "\n"; // d is an integer between 0 - 15
        for (int k = 0; k < size; k++) // close all the 16 files
	{
		f[k].close();
	}

And when I run my codes, I got this error:
Usage:
ff [-F FSType] [-V] [current_options] [-o specific_options] special ...
where ff is my output file name

[CMPITG]

I believe what you are missing is setting your stringstream back to empty before re-assiging it:

ssFileName.str ("");
ssFileName << << "N" << k << ".txt";

This is my test code and it works just fine:

#include <iostream>
#include <sstream>
#include <fstream>

using namespace std;

int main( int argc, char **argv )
{
    int size = 3;
    ofstream f[size];
    stringstream ssFileName;

    for (int i = 0; i < size; i += 1)
    {
        ssFileName.str( "" );
        ssFileName << "N" << i << ".txt";
        cout << ssFileName.str() << endl;
        f[i].open( ssFileName.str().c_str() );
    }

    for (int i = 0; i < size; i++)
        f[i] << "I received something!" << i << endl;

    for (int i = 0; i < size; i++)
        f[i].close();
    
    return 0;
}

[Mz3g]

I did exactly as u said and I still got the same error:

Usage:
ff [-F FSType] [-V] [current_options] [-o specific_options] special ...

[CMPITG]

Could you please tell me the commands you used to compile and run your program?

[jonsca]

Have you named your executable the same name as some other system software? It doesn't seem like your code has any error message like that. Try renaming your program.

[Mz3g]

Thank u both of u..
I used this code:
g++ -o ff ff.cpp

but it works now after I changed the ff to other name. thanks alot :)