Copying contents of one file to another leaves the other file empty - c++

Question

I'm trying to copy the contents of document1.txt to document2.txt using this simple program:
int main() {
ifstream in("document1.txt");
ofstream out("document2.txt");
string str;
while(getline(in,str))
out<<str;
}
But, when I run the program, I find that document2.txt is still empty.
What could be wrong?

Answer 1

ifstream in("document1.txt");
ofstream out("document2.txt");
string str;
while(getline(in,str))
{
out<<str;
}
in.close(); // <---
out.close(); // <---
There is a function to close it. Please check this: ifstream and ofstream.

Answer 2

"I have manually created document1.txt and document2.txt"
In case you are running your program directly from Visual Studio, note that the working directory is set to $(ProjectDir) by default, i.e. these files must be placed at the same directory where your project file (.vcproj / .vcxproj) is.
You could either place them to the appropriate directory or specify the full path, for example place them directly to C: and in code do:
ifstream in("C:\\document1.txt");
ofstream out("C:\\document2.txt");
This is something you would notice if you outputted something in case of an error while opening:
if (!out.is_open())
{
std::cout << "ERROR: Can not open document2.txt" << std::endl;
return -1;
}
Note that in this case you don't actually need to flush any buffer, neither close the streams explicitly. All of this will happen automatically when these objects are destructed, i.e. when the execution goes out of scope.

Answer 3

ifstream document1("document1.txt");
ofstream document2("document2.txt");
string str;
getline(document1, str);
document2<< str<< endl;
document1.close();
document2.close();
Try this code. It works for me.

Answer 4

test.cpp
#include <iostream>
#include <fstream>
using namespace std;
int main() {
ifstream in("document1.txt");
ofstream out("document2.txt");
string str;
while(getline(in,str))
out<<str<<endl;
}
document1.txt
aaaaaaaa
bbb bbb
c c c c
d
under command line you can do
$g++ test.cpp -o test.out
$test.out
And then you will get document2.txt
aaaaaaaa
bbb bbb
c c c c
d
P.S. All the code tested under Mac and Linux
P.S. if you change 9th line of test.cpp from out<<str<<endl; to out<<str;
document2.txt would becomes
aaaaaaaabbb bbbc c c cd
because the getline(in,str) function would extracts characters from in and stores them into str until '\n' or end-of-file is found.
Which means str does not contains '\n'. You need to add '\n' by yourself.
P.S. under C++, as LihO says, you don't need to close in and out, since in and out would be closed at line 10 }
Also, you don't need to flush when you execute line 9, since endl has flush function.