Regarding files streams

[vinaynaikwad]

Is there anything wrong with the following piece of code?
I have one original file at some location. I copy it's contents excluding the blank lines to some temp file in the same location. Then I delete the original file and rename the temp file with the name of the original file. And at last print the contents of the renamed file.

The problem is my code gets struck while printing the final contents of the file. It doesn't come out of the loop. Just keeps printing empty lines.
Please help.

String activeFile = "/var/tmp/active.txt";
String tempFile = "/var/tmp/temp.txt";

ifstream file_active;
file_active.open(activeFile);
char oneLine[255];

if (file_active.is_open())
{
	cout << "File open successful" << endl;
	
	ofstream temp_active(tempFile);
	
	while (!file_active.eof())
	{
		memset (oneLine, '\0', sizeof(oneLine));
		file_active.getline(oneLine, 255);

		if (oneLine.is_empty())
		{
			continue;
		}

		temp_active << oneLine << endl;
	}

	file_active.close();
	temp_active.close();
}
else
{
	cout << "Error opening file" << endl;
}

//Remove the original file i.e. activeFile
int status = removeFile(activeFile);

if (status)
{
	//Rename temp file to original file
	renameFile(tempFile, activeFile);
}

cout << "The contents of the file finally are: "

char finalLine[255];
file_active.open(activeFile);

//The code is not printing the contents of this file
//Gets struck inside the loop printing empty lines.
if (file_active.is_open())
{
	while(!file_active.eof()) // To get you all the lines.
    	{
		memset(finalLine, '\0', sizeof(finalLine));
		file_active.getline(finalLine,255);
		cout << finalLine << endl;
	}
}

[Cubbi]

"while not eof" is always an error, but in this case, it's worse than usual.

To print a file line by line, do this:

string finalLine;
while(getline(file_active, finalLine))
    cout << finalLine << '\n';

[vinaynaikwad]

@Cubbi,

But the same code works fine sometimes. And sometimes it gets struck, though it's not very clear to me when it gets struck.
Will you please elaborate on why it's going to infinite loop?

[fdxuwei]

I doubt how your programme can compile success？
you defined ：char oneLine[255]，but type of char don't have a member function called is_empty()

[Cubbi]

Will you please elaborate on why it's going to infinite loop?

The infinite loop happens when the stream has its badbit or failbit flags on (the flags are never checked and never cleared). The array version of getline() that's called here sets the failbit when it extracts the specified number of characters minus one (254) without encountering the end of line.

(btw, memset() is completely unnecessary: even when reading past the end of file, which is what this loop does when it doesn't go infinite, istream::getline() writes a null character to the first position of the array)

[vinaynaikwad]

@fdxuwei
I forgot one line of code there.

It's actually as below:

String tempLine = (String)oneLine;

And then tempLine is used.

I just wanted to avoid writing more code. So skipped that line.

[fdxuwei]

The book "The c++ standard library", on page 519, said : "Note that you always have to clear error bits explicitly. In C it was possible to read characters after a format error. For example, if scanf() failed to read an integer, you could still read the remaining characters. Thus, the read peration failed, but the input stream was still in a good state. This is different in C++. If failbit is set, each following stream operation is a no-op until failbit is cleared explicitly"

so, you shoud call file_active.clear to clear the previous eof error bit before the second call to file_active.open

[vinaynaikwad]

@Cubbi,

When i use getline function as suggested by you, I am getting the following error:

Error: Could not find a match for std::getline<std::charT, std::traits, std::Allocator>(std::ifstream, String)

My code is as below:

#include <fstream.h>
#include <iostream.h>

ifstream inActive;
inActive.open(file);

String finalLine;

while (getline(inActive, finalLine))
{
	cout << finalLine << endl;
}

inActive.close();

Do i need to include any other header for this?

[Darkmaster]

#include <string>

also you are missing all the std namespaces

[vinaynaikwad]

@Darkmaster

I included the following:

#include <string>
using namespace std;

Even then I am getting same error. By the way, I am compiling in Solaris.

[vinaynaikwad]

Any problem if I use the getline function like this??

while (inActive.getline(finalLine, 255))
{
	cout << finalLine << endl;
	memset (finalLine, '\0', sizeof(finalLine));
}

Will this avoid the EOF problem ??

[Cubbi]

vinaynaikwad wrote:

By the way, I am compiling in Solaris.

I am too

vinaynaikwad wrote:

String finalLine;

there's your error, the correct line is
string finalLine;

[vinaynaikwad]

@Cubbi,

Yes it worked. Thank you.