cout behaviour

[RadWayne]

I'm opening a file and reading through it line by line, printing each line to the console. If I do not put some sort of newline character at the end of each call to cout, only one line is printed.

This code works as expeted

int main(int argc, char* argv[])
{
	if (argc < 2)
		return 0;
	std::ifstream file(argv[1]);
	if (!file.is_open())
	{
		std::cout<<"Problem opening file: " << argv[1] << "\n";
		return 1;
	}

	std::string in;
	while (std::getline(file,in))
	{
		std::cout<<in<<"\n";//with a new line
	}
}

However, changing the cout in the while loop to look like this

std::cout<<in;

causes only one line of the file to be printed to the console.

What causes this?

[Chervil]

causes only one line of the file to be printed to the console.

Don't you mean it causes all of the lines of the file to be printed together on a single line?

getline() discards the newline which it reads from the file.
http://www.cplusplus.com/reference/string/string/getline/

[RadWayne]

I have a file test.txt that contains

line 1
line 2
line 3

Running the above code with the new line results in

line 1
line 2
line 3

Without the newline results in

line 3

[Chervil]

That seems odd.

When I try it I get:

line 1
line 2
line 3

and

line 1line 2line 3

Did you change anything else apart from the "\n" ?

Maybe you could post your code which gives this output:

line 3

[RadWayne]

Here is exactly what I have

#include <iostream>
#include <fstream>
#include <string>

int main(int argc, char* argv[])
{
	if (argc < 2)
		return 0;
	std::ifstream file(argv[1]);
	if (!file.is_open())
	{
		std::cout<<"Problem opening file: " << argv[1] << "\n";
		return 1;
	}

	std::string in;
	while (std::getline(file,in))
	{
		std::cout<<in;//<----
	}
}

Compiling with g++ -std=c++14 and gcc version 5.3.0 (GCC).

[Chervil]

Still works ok for me. The only way I can get just a single line (the last line) from the file is if I change the code in some way (such as adding an unwanted semicolon on line 17).

[Chervil]

I had an idea. If you use a text file created on a windows system and try to use it on a non-windows system, the difference in line endings may cause strange behaviour,

As an experiment, you could try this:

#include <iostream>
#include <fstream>
#include <string>

int main(int argc, char* argv[])
{
    if (argc < 2)
        return 0;
    std::ifstream file(argv[1]);
    if (!file.is_open())
    {
        std::cout<<"Problem opening file: " << argv[1] << "\n";
        return 1;
    }

    std::string in;
    while (std::getline(file,in))  
    {
        std::cout << int (in.back()) << '\n';
        std::cout << in << '\n';
    }

}

With the same input file, this is the output I get:

49
line 1
50
line 2
51
line 3

[RadWayne]

If you use a text file created on a windows system and try to use it on a non-windows system, the difference in line endings may cause strange behaviour

This was it!