Thread: Unwanted char/byte when joining files

Hello everyone.

I wrote the a piece of code to join three files but there is an unwanted char/byte "ÿ" that shouldn't exist but does.

The result is something like

Code:

*FILE1**FILE2*ÿ*FILE3*ÿ

Instead of

*FILE1**FILE2**FILE3*

Any help would be appriecated.

My two questions are: Why is it there, and how can I stop it from appearing.

Code:

	ifstream in("Text1.txt", ios::in | ios::binary);
	ofstream out("Text3.txt", ios::out | ios::app | ios::binary);

	if(in.is_open() && out.is_open())
	{
		while(!in.eof())
		{
			out.put(in.get());
		}
	}
	in.close();
	out.close();
    
	ifstream in2("Text2.txt", ios::in | ios::binary);
	ofstream out2("Text3.txt", ios::out | ios::app | ios::binary);

	if(in2.is_open() && out2.is_open())
	{
		while(!in2.eof())
		{
			out2.put(in2.get());
		}
	}
	in2.close();
	out2.close();

Originally Posted by grumpy

The two loops of the form

Code:

while (!in.eof())
{
    out.put(in.get());
}

are the culprits. If in.get() return a value indicating end of file, that value will be output before the loop ends. The solution is not to loop looking for end of file, and to test the value returned by "in.get()" BEFORE outputting it.


There is a FAQ here explaining why the equivalent if C (involving a "while (!feof(file))" loop where the body reads from the file) is a bad idea if you want more information.

Thanks Grumpy.

I'm a novice who is amazed I even put the two loops together at all. How do I test get? I tried a whole bunch of if statements and stuff but nothing worked. Also, would you mind sharing a link to the FAQ you mentioned?

Originally Posted by Elysia

Essentially, the problem is that eof() only becomes true AFTER you've made a read that failed.
So, assume there is one byte left in the file. eof() returns false, get() gives your char and everything is fine.
Next iteration, eof() still returns false, get() fails and you output garbage to your file. It is for now that eof() signals true.

Thanks Elysia.

I kinda get what you mean but not enough to know how to correct it. What should I do?

Originally Posted by Elysia

You basically test if the read succeeded:

Code:

char c;
while (in.get(c))
    out.put(c);

If in.get(c) fails (i.e. you're reading beyond the end of the file), then the stream will be put into an error state. You can check if a stream is good or not by simply checking it as if it were a boolean, which is what the loop does.

Thanks a lot Elysia.