How to detect an empty file in C++? [duplicate]

Question

I am trying to use eof and peek but both seems not to give me the right answer.

if (inputFile.fail()) //check for file open failure
{
    cout << "Error opening file" << endl;
    cout << "Note that the program will halt" << endl;//error prompt
}

else if (inputFile.eof())
{
    cout << "File is empty" << endl;
    cout << "Note that program will halt" << endl; // error prompt
}
else
{
    //run the file
}

it cannot detect any empty file using this method. If i use inputFile.peek instead of eof it would make my good files as empty files.

Answer 1

Use peek like following

if ( inputFile.peek() == std::ifstream::traits_type::eof() )
{
   // Empty File

}

Answer 2

I would open the file at the end and see what that position is using tellg():

std::ifstream ifs("myfile", std::ios::ate); // std::ios::ate means open at end

if(ifs.tellg() == 0)
{
    // file is empty
}

The function tellg() returns the read (get) position of the file and we opened the file with the read (get) position at the end using std::ios::ate. So if tellg() returns 0 it must be empty.

Update: From C++17 onward you can use std::filesyatem::file_size:

#include <filesystem>

namespace fs = std::filesystem; // for readability

// ...

if(fs::file_size(myfile) == 0)
{
    // file is empty
}

Note: Some compilers already support the <filesystem> library as a Technical Specification (eg, GCC v5.3).