Thread: Reading from file stream using ifstream object and storing in a map

Code:

void loadGames(){
    std::ifstream load("Gamelist.gl");
    num_holder;
    title_holder;
    hours_holder;
    load.getline(num_holder, 1, ' ');
    load.getline(title_holder, 20, ' ');
    load.getline(hours_holder, 5);
    Games[num_holder].title = title_holder;
    Games[num_holder].hoursPlayed = hours_holder;
}

I'm having some trouble getting this to work. At first I tried to read directly into an int, std::string and double with no luck so I tried reading into character arrays and converting them to ints and std::strings with even less luck. I think this is probably not a good way to go about this and there has to be a more efficient way. Can someone help please?

P.S. Posting the complete code is unnecessary but here is the definition of the std::map container I'm placing the values in just in case:

Code:

struct Game{
    std::string title;
    double hoursPlayed;

};

typedef std::map<int, Game> gameMap;
gameMap Games;

What are these statements?

Code:

num_holder;
title_holder;
hours_holder;

Based on subsequent code, it looks like they are variables, but you didn't show their declarations, plus writing them like this results in code that has no net effect. You could very well have written:

Code:

;
;
;

Did you perhaps intend to declare (and hence define) the variables instead?

What does the file itself look like?

istream::getline - C++ Reference

Code:

    num_holder;
    title_holder;
    hours_holder;
    load.getline(num_holder, 1, ' ');
    load.getline(title_holder, 20, ' ');
    load.getline(hours_holder, 5);

What exactly are the first 3 lines doing?
Are they declaring char arrays of a suitable size, or is this just down to your creative editing?

Passing 1 to getline() makes no sense, as it stores (n-1) (ie, ZERO) characters.

The problem with incremental parsing happens when the file is malformed, and you lose sync with what is in the file compared to what you expect.
Say for example someone tries to enter a 25 character title_holder. The excess characters will get stored in hours_holder.

If you're pretty sure that space is a good delimiter in your file when you generate it, then perhaps something like this.

Code:

#include<iostream>
#include<fstream>
#include<string>
#include<sstream>
using namespace std;
int main()
{
    string line;
    string one, two, three;
    ifstream load("Gamelist.gl");
    while ( getline(load,line) ) {
        istringstream is(line);
        if ( is >> one >> two >> three ) {
            cout << one << "," << two << "," << three << endl;
        }
    }
}

Everything is a std::string, so no messy char arrays where you have to guess the length is "good enough".

Results

Code:

$ cat Gamelist.gl 
1 hello world
2 this_is_a_very_long_string and_this_is_pretty_long_as_well
$ ./a.out 
1,hello,world
2,this_is_a_very_long_string,and_this_is_pretty_long_as_well

Originally Posted by phantomotap

No. You did not say that. You said you had tried a couple of different things. It is natural for us to assume that what you posted is what you have written.

This forum has some awesome skill in the form of its community, but we can't read minds.

Please show us exactly what you are trying to do exactly as you are trying to do it or we can only speculate about what is going wrong.

Soma

Well, I'm sorry. "At first I tried to read directly into an int, std::string and double with no luck so I tried reading into character arrays and converting them to ints and std::strings with even less luck. I think this is probably not a good way to go about this and there has to be a more efficient way." seemed pretty straightforward to me. But I did say I don't have a clue how to go about it so I cannot show you exactly how I am trying to do it. I only included the code as a substitute for a long and potentially confusing explanation.

EDIT:

Originally Posted by Salem

if ( is >> one >> two >> three ) {
cout << one << "," << two << "," << three << endl;
}
[/code]

My best guess is that this places the contents of is into one up until the first whitespace, two up until the next, and then three up until the next (end of file). Is that correct? If so, I think that would work perfectly.

EDIT: Actually I overlooked something, since variables one and three need to be int and double respectively. Is there something similar to istringstream that applies to numbers?

Why are you casting to std::string when it already is a std::string?
Games[num].title = std::string(title_holder);