Reading File in C++

I am unable to figure out why my code is not able to open and read a file. What am i missing?

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int m开发者_开发问答ain (int argc, char * const argv[]) 
{
    string line;
    ifstream myfile ("input_file_1.txt");
    if (myfile.is_open())
    {
        while (!myfile.eof())
        {
            getline (myfile,line);
            cout << line << endl;
        }
    }
    else
    {
        cout << "Was unable to open the file" << endl;
    }

    return 0;
}

The file "input_file_1.txt" is int he same directory as my .cpp file and it has read permissions. I even gave gave it 777 permissions and i was unable to read it.

Can anyone tell me what i am doing wrong? I really cannot figure it out....

• Try to use full path for the file
• The default location to look for the file is where the executable is , not where the source is.

How and where do you execute your program? From a IDE? Can you run the program from the same directory where you have your text file. Another possibility is to use an absolute path to the file.

If you don't specify a path, the library will attempt to load the file from the current directory. You need to make sure that this is where the file is.

Also, you might not be able to open the file if it is opened in an exclusive manner by another program. Ensure that it is not still open in another program such as your editor.

Other Problems:

Explicitly testing for EOF is usually wrong.
The last valid read (getline() here) reads up-to but no past the EOF. You then print the line. Then restart the loop. These test for eof() does not fail (as it has not read past the EOF). You then enter the loop body and attempt to read the next line (with getline()) this fails as there are 0 bytes left to read (thus leaving the value of line in an undefined state). You then print out line (undefined value) and a newline character.

    while (!myfile.eof())
    {
        getline (myfile,line);
        cout << line << endl;
    }

A correct version of a loop reading a file is:

    while (getline (myfile,line))
    {
        cout << line << endl;
    }

This works because the getline() returns a reference to a stream. A stream used in a boolean context (like a while condition) tests to see if the stream is in a bad state (ie it test for EOF and other bad situations) and returns an object that can be used correctyl in the context. If the state of the stream is OK then a successful read has happened and the loop is entered (thus allowing you to print the line).

The binary created from your code (including your cpp) is executed somewhere different from your code is, probably a "bin"-folder. You schould put the file into the same folder as your executable.