Question

I cannot figure out why getline is working in one X-Code project but not in another. The error “No matching function for call to ‘getline’.
When I make a single cpp file it compiles with no issues.

  // reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main () {
      string line;
      ifstream myfile ("example.txt");
      if (myfile.is_open())
      {
        while ( myfile.good() )
        {
          getline (myfile,line);
          cout << line << endl;
        }
        myfile.close();
      }

  else cout << "Unable to open file"; 

  return 0;
}

I would really appreciate some assistance. I am just learning and the example above came from my test book.

Answer 1

The code is noisy and incorrect. The correct standard idiom is like this:

#include <fstream>   // for std::ifstream
#include <string>    // for std::getline and std::string

std::ifstream myfile("example.txt");

if (!myfile) { /* error, die */ }

for (std::string line; std::getline(myfile, line); )
{
    std::cout << "Read one line: '" << line << "'\n";
}

Correctness:

• You must check the success of the input operation before consuming the input. To do otherwise may be UB, and certainly never correct.

• [Thanks @James for pointing this out:] good() doesn’t check if a file was opened. You could use either !myfile.fail() or myfile.is_open(), but just don’t bother (see below).

Noise:

• The ifstream constructor takes the filename and opens the file already. Use it.

• The ifstream cleans up in its destructor, no need to do that explicitly. Use tight scoping to close the file as soon as you’re done with it.

• Don’t leak line into the ambient scope if you don’t need it.

• No need for good() (or any of the correct alternatives). Just evaluate the ifstream object in a boolean context to see if the file was opened successfully.