Binary reader not triggering eof bit when reading exact number of bytes - c++

Question

I am writing images to a binary file using this code:
std::ofstream edgefile("C:\\****\\edge.bin", std::ofstream::binary | std::ofstream::app | std::ofstream::out);
Mat edges;
Canny(bilat, edges, cthr1, cthr2, 3); //cany sliders
if (writeedge){
int rows = edges.rows;
int cols = edges.cols;
edgefile.write(reinterpret_cast<const char *>(&rows), sizeof(int));
edgefile.write(reinterpret_cast<const char *>(&cols), sizeof(int));
edgefile.write(reinterpret_cast<char*>(edges.data), edges.rows*edges.cols*sizeof(uchar));
cout << "writen r:" << rows << "C: " << cols << "Bytes: " << edges.rows*edges.cols*sizeof(uchar) << endl;
}
And then reading the same images with this:
std::ifstream infile;
int main(int argc, char* argv[])
{
int * ptr;
ptr = new int;
int rows;
int cols;
infile.open("C:\\****\\edge.bin", std::ofstream::binary | std::ofstream::app | std::ofstream::in);
while (!infile.eof())
{
infile.read(reinterpret_cast<char*>(ptr), sizeof(int));
rows = *ptr;
infile.read(reinterpret_cast<char*>(ptr), sizeof(int));
cols = *ptr;
Mat ed(rows, cols, CV_8UC1, Scalar::all(0));
infile.read(reinterpret_cast<char*>(ed.data), rows * cols * (sizeof uchar));
cout << "writen r: " << rows << " C: " << cols << " Bytes: " << rows * cols * (sizeof uchar) << endl;
imshow("God Knows", ed);
cvWaitKey();
}
infile.close();
return 0;
}
The images are read accurately however eof bit is not triggered at the end thus multiplying the last ptr value and reading another blank image at the end. After this the cycle ends. How can I check if the next bit is EOF bit without resetting the currently read position?
(I know that if 1 more byte would be read it would trigger the EOF bit)

Answer 1

The EOF bit is set after you try to read past the end of the file, that's just how streams work.
You can easily restructure the main loop to check the status after the first read. This works because the return value from read is a reference to the stream, and casting the reference to bool checks whether the stream is still in a good status (i.e. no EOF).
while (infile.read(reinterpret_cast<char*>(ptr), sizeof(int)))
{
// ...