Prevent the loop from reading the last file line twice

[std10093]

I know how to do it in C, but in C++?

Here is my code. Let the variables be of type double.

while(infile) // Will read the last line twice
    {
    	if(!N)	//Read first line of file
    	{
    		infile >> d;
    		infile >> N;
    		infile >> epsilon;
    		infile >> t;
    	}
    	else
    	{
    		double hCoords[P.getD()];
    		for(size_t i = 0 ; i < P.getD() ; ++i)
    			infile >> hCoords[i];

    		//Read min distance of origin
    		infile >> d;
    	}
    }

[cyberfish]

You can read into a temporary variable first, then test for eof.

If eof is set (meaning last read value is invalid), just break out of the loop, otherwise continue.

[vart]

actually you should check result of each read to be sure it was successful instead of checking the stream state postfactum

while(infile) // Will read the last line twice
    {
        if(!N)  //Read first line of file
        {
            if(infile >> d >> N >> epsilon >> t)
            {
              //first line read OK
            }
            else
            {
              //error occurred - notify and exit
            }
        }
...

[std10093]

Vart I am not looking for an error, but for the EOF.

Cyberfish, with this code

while(infile) // Will read the last line twice
    {
    	if(!N)	//Read first line of file
    	{
    		infile >> d;
    		P.setD(d);
    		infile >> N;
    		infile >> epsilon;
    		infile >> t;
    	}
    	else
    	{
    		double hCoords[P.getD()];
    		for(size_t i = 0 ; i < P.getD() ; ++i)
    		{
    			infile >> d;
    			//std::cout << d << " " << i << std::endl;
    			//if(d==EOF)break;
    			hCoords[i] = d;
    			std::cout <<hCoords[i]  << "\n";
    		}

    		//Read min distance of origin
    		infile >> d;
    		std::cout << hCoords[0] << " " << hCoords[1] << " "
    				<< hCoords[2] << " " << d << "\n";
    	}
    }

I read as expected and I read the line twice, which is

-0
-0
-1
-0 -0 -1 -0
0
-1
0
0 -1 0 0
-1
-0
-0
-1 -0 -0 -0
0.57735
0.57735
0.57735
0.57735 0.57735 0.57735 0.57735
0.57735
0.57735
0.57735
0.57735 0.57735 0.57735 0.57735

Here is my file.

3 4 0.1 3
-0.000000000 -0.000000000 -1.000000000 -0.000000000
 0.000000000 -1.000000000  0.000000000  0.000000000
-1.000000000 -0.000000000 -0.000000000 -0.000000000
 0.577350269  0.577350269  0.577350269  0.577350269

If I uncomment the two lines of code, I am getting this

-0
-0
-0 -0 -1.71101e-41 -0
0
0 -0 -1.71101e-41 0
0
0 -0 -1.71101e-41 -0
-0
-0
0.57735
-0 -0 0.57735 0.57735
0.57735
0.57735
0.57735
0.57735 0.57735 0.57735 0.57735

Moreover, I tried infile.eof(), but with no use at all.

[tabstop]

You seem to know that infile can return false when the previous read failed, as that's the point behind "while (infile)" in the first place. But it's not prescient -- it doesn't know that the next call is going to fail, it can only tell you that the previous call failed. If you've already (tried to) process that previous read then it's too late. Check the state of infile before you do anything.

[oogabooga]

You actually have to "hit" the end-of-file for it to be detected. If you have the filesize info elsewhere, you can use that to control the loop. I don't know what your data is, but perhaps N is the number of records in the file? If so, you could write:

//Read first line of file
infile >> d;
P.setD(d);
infile >> N;
infile >> epsilon;
infile >> t;

for (size_t n = 0; n < N && infile; n++)
{
    double hCoords[P.getD()];
    for (size_t i = 0; i < P.getD(); ++i)
        infile >> hCoords[i];

    // Read min distance of origin
    infile >> d;

    // Display data
    for (size_t i = 0; i < P.getD(); ++i)
        std::cout << hCoords[i] << ' ';
    std::cout << d << '\n';
}

BTW, your variable names ain't too great.

[vart]

Vart I am not looking for an error, but for the EOF.

And what you will do in case of error?

[std10093]

That did the trick.
I explain the variables when I declare them, but ok, I see your point.

vart, I do the check when I open the file. If the file has opened ok, then I procede with parsing it.

[vart]

vart, I do the check when I open the file. If the file has opened ok, then I procede with parsing it.

You mean your file reading never fails? File could never be corrupted or overwritten by too smart user? or by mistake with some garbage? You are to optimistic in your programming style for my taste.