Reading from file in c++ ifstream

Question

I am working on a program that reads from a file and pushes back the contents of that file into a vector. It will read until the file reaches a space and push that string into a vector, then continue after the space. I have written this code.

  ifstream inFile;
            inFile.open("message1.txt");
            if (inFile.fail()) {
                    cerr << "Could not find file" << endl;
            }
            while (inFile >> S) {
                    code1.push_back(S);
            }

I am just confused about the while (inFile >> S) actually does. I understand that it reads from the inFile until it reaches the end of file. But what does the inFile >> S condition actually do? Thanks for your time.

Answer 1

The expression inFile >> S reads a value into S and will return inFile.

This allows you to chain variables together like infile >> a >> b >> c;

Since this inFile is being used in a bool context, it will be converted to bool. And iostream objects are defined to convert to a bool that's true if and only if the object has no current error state.

Answer 2

What the inFile >> S does is take in the file stream, which is the data in you file, and uses a space delimiter (breaks it up by whitespace) and puts the contents in the variable S.

For example:

If we had a file that had the follow contents

the dog went running

and we used inFile >> S with our file:

ifstream inFile("doginfo.txt")
string words;
while(inFile >> words) {
   cout << words << endl;
}

we will get the following output:

the
dog
went
running

The inFile >> S will continue to return true until there are no more items separated by whitespace.