Strange result when editing file in C++ - c++

Question

For a couple of weeks now, I have been developing a random class generator for the Xbox game Call of Duty: Modern Warfare 3. In this game, different weapons have different levels, which increase as you use the weapon more. I am storing the weapons and their levels in a text file, which store the data on separate lines with the format
weapon-weapon_level
So the M4A1 with weapon level 8 would look like:
m4a1-8
(The weapons are all in lowercase with no punctuation or spaces).
I have already written methods for creating the file and reading the file, but I want a method to edit the file, so the user enters the weapon whose level they want to change, then the new level. Here's what I have so far: (The file is called "weaponlevels.txt")
void WeaponLevelFile::editFile()
{
string line;
string weapon;
string weaponent;
string weaponlevel;
string temp;
cout<<"Please enter the weapon whose level you wish to change. Enter the name in lowercase, with "<<endl;
cout<<"no spaces or punctuation except full stops. E.g. SCAR-L becomes scarl and Barrett .50cal "<<endl;
cout<<"becomes barrett.50cal."<<endl;
cin>>weaponent;
cout<<"Please enter the new weapon level."<<endl;
cin>>temp;
ifstream infile("weaponlevels.txt");
ofstream outfile("weaponlevels.txt");
while (getline(infile, line))
{
istringstream ss(line);
getline(ss,weapon,'-');
if (weapon == weaponent)
{
ss>>weaponlevel;
weaponlevel=temp;
outfile<<weaponlevel<<endl;
infile.close();
outfile.close();
}
}
}
This method does not work however; all it does is wipe the file (so the file is blank). Why does it do this, and what is a better method?
EDIT:
#stardust_'s answer worked the best, but still didn't completely do it. Here is the code:
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
int main()
{
string temp;
string line;
string weapon;
string weaponent;
string weaponlevel;
cout<<"enter weapon"<<endl;
cin>>weaponent;
cout<<"enter level"<<endl;
cin>>temp;
ifstream infile("weaponlevels.txt");
std::string in_str((std::istreambuf_iterator<char>(infile)),
std::istreambuf_iterator<char>());
infile.close();
stringstream infile_ss(in_str);
while (getline(infile_ss, line))
{
istringstream ss(line);
getline(ss,weapon,'-');
if (weapon == weaponent)
{
ss>>weaponlevel;
weaponlevel=temp;
infile_ss<<weaponlevel<<endl;
}
}
ofstream outfile("weaponlevels.txt");
outfile << infile_ss.str();
outfile.close();
}
It modifies the right part of "weaponlevels.txt", but doesn't completely do it. if i enter m4a1 as the weapon and 7 as the weapon level, instead of becoming m4a1-7 it becomes:
7
a1-3

Answer 1

After quite a lot of work, here's what worked:
#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;
int main()
{
string temp;
string line;
string weapon;
string weaponent;
string weaponlevel;
cout<<"enter weapon"<<endl;
cin>>weaponent;
cout<<"enter level"<<endl;
cin>>temp;
ifstream infile("weaponlevels.txt");
std::string in_str((std::istreambuf_iterator<char>(infile)),
std::istreambuf_iterator<char>());
infile.close();
stringstream infile_ss(in_str);
ostringstream out;
while (getline(infile_ss, line))
{
istringstream ss(line);
getline(ss,weapon,'-');
out << weapon << '-'; // Write the first part of the line.
if (weapon != weaponent)
{ // Not the correct weapon so just write the original information.
ss >> weaponlevel;
out << weaponlevel << endl;
}
else
{ // Found the desired weapon, change the level.
out << temp << endl;
}
}
I loaded the whole string into an ostringstream and found the weapon within the string.

Answer 2

Have you tried using pointers to search through the file for a specific string to replace? I have yet to write a program that uses this myself, but I know it's pretty common. Otherwise you'll just be overwriting the entire file.
Note that I'm not entirely certain whether you have used pointers in your code for this purpose because, as I stated above, I have yet to use this myself. However, from what I saw, I don't think you did. Just correct me if I'm wrong.

Answer 3

There are many problems with your code. You are opening a file twice. you are closing the ifstreams in a loop while reading them (?). ...
However algorithm wise you can open the file for reading, read the whole thing to a string, close the file, modify the string, open the file for writing, write the string, close the file.
int main()
{
cin>>temp;
ifstream infile("weaponlevels.txt");
std::string in_str((std::istreambuf_iterator<char>(infile)),
std::istreambuf_iterator<char>());
infile.close();
stringstream infile_ss(in_str);
while (getline(infile_ss, line))
{
istringstream ss(line);
getline(ss,weapon,'-');
if (weapon == weaponent)
{
ss>>weaponlevel;
weaponlevel=temp;
infile_ss<<weaponlevel<<endl;
}
}
ofstream outfile("weaponlevels.txt");
outfile << infile_ss.str();
outfile.close();
}

Answer 4

instead of
ifstream infile("weaponlevels.txt");
use
ifstream infile("weaponlevels.txt", ifstream::in)