Segfault from hflip

Question

For some reason when I run this code I get a segfault. What it does is reads a PGM file from input and flips it horizontally.

Here is what I believe is the offending code:

for (i = pixels.size()-1; i = 0; i--){ // this loop takes the final value of the original vector and puts it into the first spot in the new hflip vector, and continues onwards
    flippy.push_back(pixels[i]);
}

cout << "P2" << endl << numColumns << " " << numRows << endl << "255" << endl;
while (p < pixTotal){
    for (int z = 0; z < numRows; z++){
        cout << flippy[p] << " ";
    }
    cout << endl;
    p++;

}

Answer 1

I assume the vector pixels represents each row in your matrix. Then to flip all values in the vector, you can simply use std::reverse_copy like this:

std::vector<uint8_t> flippy;
flippy.resize(pixels.size());
std::reverse_copy(pixels.begin(), pixels.end(), flippy.begin());

You need to do this for each row. You can then output each flipped row after each reverse so that the vector 'flippy' only represents the current row in operation.

Answer 2

You have

for (i = pixels.size()-1; i = 0; i--)

the middle should be

i>=0

not

i=0