Reading from a text file to populate an array

Question

The goal I am going for is to store values into a text file, and then populate an array from reading a text file.

At the moment, I store values into a text file;

Pentagon.CalculateVertices();//caculates the vertices of a pentagon

ofstream myfile;
myfile.open("vertices.txt");
for (int i = 0; i < 5; i++){
    myfile << IntToString(Pentagon.v[i].x) + IntToString(Pentagon.v[i].y) + "\n";
}
myfile.close();

I have stored the values into this text file, now I want to populate an array from the text file created;

for (int i = 0; i < 5; i++){
    Pentagon.v[i].x = //read from text file
    Pentagon.v[i].y = //read from text file
}

this is all I have for now; can someone tell me how you can achieve what the code says.

LogicStuff · Accepted Answer · 2015-03-22 21:53:38Z

3

You don't need to convert int to std::string nor char*.

myfile << Pentagon.v[i].x << Pentagon.v[i].y << "\n";
// this will add a space between x and y coordinates

Read like this:

myfile >> Pentagon.v[i].x >> Pentagon.v[i].y;

<< and >> operators are the basics of streams, how come you haven't come across it?

You could also have a custom format, like [x ; y] (spaces can be omitted).

Writing:

myfile << "[" << Pentagon.v[i].x << ";" << Pentagon.v[i].y << "]\n";

Reading:

char left_bracket, separator, right_bracket;
myfile >> left_bracket >> Pentagon.v[i].x >> separator << Pentagon.v[i].y >> right_bracket;

// you can check whether the input has the required formatting
// (simpler for single-character separators)
if(left_bracket != '[' || separator != ';' || right_bracket != ']')
    // error

edited Mar 22, 2015 at 21:53

answered Mar 22, 2015 at 21:33

LogicStuff

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8 Comments

Moynul Over a year ago

So in order for me to store values in a text file, they can be any 'type'? They do not need to be strings? I come from a background, where the basics were skipped.

LogicStuff Over a year ago

They could accept even custom classes if you overload the operators.

Moynul Over a year ago

That makes sense, or we would not be able to have complex programs. A question, ">>" is giving me errors., do I need

Failed Scientist Over a year ago

@Moynul Have you used std namespace etc?

Moynul Over a year ago

@TalhaIrfan At the top I have 'using namespace std' to let the compiler know in advance.

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