C++ Creating/Parsing Text File Into a Function

Question

I'm trying to take input from a text file to call a function. The function takes 3 int paramaters. Each line in the text file will include each int followed by a space. How do I parse each line, call a function using integers from each line, and then exit the loop and close the file? Any help would be greatly appreciated.

// Here is what the contents of the text file will look like
1 2 3
4 5 6 
7 8 9
10 11 12

// here is the function
void readValues(int1, int2, int3)
{
    // do something
}

// open text file and parse input. if it does not exist, create file

ifstream file("test.txt", fstream::in | fstream::out | fstream::trunc);

while (file.eof())
{

    int a, b, c;
    file >> a >> b >> c >> std::endl;
    readValues(a, b, c); // first iteration would be readValues(1, 2, 3)

    if(file.eof())
    {
         break;
    }
}

file.close();

What about this code doesn't work? Include errors, for example, that the compiler outputs. http://youtube.com/watch?v=786PavIEAOQ — Don Larynx, May 04 '15 at 18:45
never use `eof()` to control a loop. http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong — NathanOliver, May 04 '15 at 18:45
Also `while (file.eof())` should never run if you just opened a valid file. — NathanOliver, May 04 '15 at 18:46
I was having issues building the program. I didn't need the std::endl statement. — user3781214, May 04 '15 at 18:52

score 1 · Answer 1 · answered May 04 '15 at 18:51

1

If you're going to read a file, you shouldn't also open it for writing (fstream::out) and truncate it (fstream::trunc).

You also shouldn't test for eof in your loop condition — there are a few occasions when eof is appropriate, but you won't encounter any for your first few years of C++ programming.

And you don't need to explicitly close the file, the destructor handles that.

Do it like this:

int main()
{
    ifstream file("test.txt");

    int a, b, c;

    while (file >> a >> b >> c)
    {
        readValues(a, b, c);
    }
}

answered May 04 '15 at 18:51

molbdnilo

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this is almost what I want. How do I create test.txt if it doesn't exist? – user3781214 May 04 '15 at 18:57
1

@user3781214 What would you read from it if it doesn't exist? – molbdnilo May 04 '15 at 19:07

C++ Creating/Parsing Text File Into a Function

1 Answers1