Return values from one of two columns, or skip every other element in an array?

Question

I'm trying to write two separate functions, both of which read from a data file, but return only one of two columns from it. (The comment isn't in the .dat file, it's just written for clarification)

//  Hours     Pay Rate
    40.0       10.00
    38.5        9.50
    16.0        7.50
    42.5        8.25
    22.5        9.50
    40.0        8.00
    38.0        8.00
    40.0        9.00
    44.0       11.75

How do I return the elements representing 'hours' in one function, and return 'pay rate' in another function?

Answer 1

Use an fstream or ifstream object and the extraction operator.

std::ifstream fin(YourFilenameHere);
double hours, rate;
fin >> hours >> rate;

The classes for these objects are in the fstream header.

Answer 2

// "hours" and "payRate" might as well be class members, depending
// on your design.
vector<float> hours;
vector<float> payRate;
std::ifstream in(fileName.c_str());
string line;
while (std::getline(in, line)) {
  // Assuming they are separated in the file by a tab, this is not clear from your question.
  size_t indexOfTab = line.find('\t');
  hours.push_back(atof(line.substr(0. indexOfTab).c_str());
  payRate.push_back(atof(line.substr(indexOfTab +1).c_str()));
}

Now you can access the i'th entry in hours by hours[i], same for payRate. Likewise you can "return one column" by returning the corresponding vector if this is really what you need.