C++ ifstream Error Checking

Question

I am new to C++ and want to add error checking to my code plus I want to make sure I\'m using good coding practices. I read a line from an ASCII file into a string using:

Answer 1

paramFile >> tmp; If the line contains spaces, this will not read the whole line. If you want that use std::getline(paramFile, tmp); which reads up until the newline. Basic error checking is done by examining the return values. For example:

if(paramFile>>tmp) // or if(std::getline(paramFile, tmp))
{
    std::cout << "Successful!";
}
else
{
    std::cout << "fail";
}

operator>> and std::getline both return a reference to the stream. The stream evaluates to a boolean value which you can check after the read operation. The above example will only evaluate to true if the read was successful.

Here is an example of how I might make your code:

ifstream paramFile("somefile.txt"); // Use the constructor rather than `open`
if (paramFile) // Verify that the file was open successfully
{
    string tmp; // Construct a string to hold the line
    while(std::getline(paramFile, tmp)) // Read file line by line
    {
         // Read was successful so do something with the line
    }
}
else
{
     cerr << "File could not be opened!\n"; // Report error
     cerr << "Error code: " << strerror(errno); // Get some info as to why
}