Missing Input Incorrectly Assigned to True Rather than False in 2d Vector

[daniel88]

Hi guys,

I posted earlier today and had my problem resolved in record time, which was great as I had been struggling with the final elements of an assignment. Having received a preview automarking I found that I had one small error. Essentially, the read() function which follows takes an input file and reads the contents into a 2d vector - a vector of boolean vectors. Preceding the series of 1s and zeroes are the number of rows and columns. For example:

4 4
0011
1100
1001
0110

My function works perfectly as long as the number of rows and columns matches the actual number of rows and columns which are presented in the data. However, if one provides a file such as this:

3 5
11011
11011

It sets the extra row to a series of 1s:

MY VERSION WHICH IS INCORRECT
3 5
11011
11011
11111

CORRECT VERSION WHICH I AM TRYING TO ACHIEVE

3 5
11011
11011
00000

Here is the code:

void bitmap::read(string filename)
{
	ifstream infile;	// declare ifstream object
	
	infile.open(filename.c_str());
    
	infile >> numrows >> numcols;
		
	grid.clear();	// before reading in new values must clear grid
	
	grid.resize(numrows, vector <bool> (numcols,false));	// resize grid with new dimensions
    
	char ch;   // read in as char 
		  
	for(int i = 0; i < numrows; i++)	// cycle through rows
	{

		for(int j=0; j < numcols; j++)	// cycle through columns
        {

                 infile >> ch;
				
				grid.at(i).at(j) = ch-'0';	
         }

	} 
	
}

I am having difficulty moving forward at the moment because as far as I can tell any extra values should be set to false as I did so when I resized the vector, setting *all* the values to false. My suspicion is that somehow I am misunderstanding the inner for loop which assigns the values. As ever any help would be greatly appreciated.

Kind regards,

Daniel

[Salem]

If you're at the end of file, then infile >> ch will return end of file, and ch will remain unchanged. So you get whatever char you last successfully read repeated for all the times input fails.

Like this IIRC

if ( infile >> ch ) {
} else {
  // end of the show, exit the loops
}

[daniel88]

Thankyou Salem!!! As a newbie who aspires to becoming an accomplished programmer, this site is truly fantastic. This is a wonderful learning tool. Thanks again, mate.

PS: As a sign of respect I am going to research the int main() vs void main() issue .