PNM Reader: Can't read some files in binary mode - c++

Question

I'm having some troubles with pnm files (which is kinda obvious or else I wouldn't be posting here XD). Thing is, my teacher asked us to develop a simple pnm reader in binary mode then print it to the screen. I'm using libEGL (a framework avaliable here). My problem is that it works only with these two images and fails with any other one.
With birch.pnm and checkers.pnm it works, but cathedral.pnm, cotton.pnm and fish_tile.pnm it just simple enters an infinite loop or throws and error.
The images are avaliable here
My code is as follows:
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include "engcomp_glib.h"
using namespace std;
struct RGB{
char red, green, blue;
};
int main(int argc, char* argv[]){
RGB **image;
RGB pixel;
//ifstream _file("..\\bin\\birch.pnm");
ifstream _file("..\\bin\\checkers.pnm");
//ifstream _file("..\\bin\\cotton.pnm");
//ifstream _file("..\\bin\\cathedral.pnm");
//ifstream _file("..\\bin\\fish_tile.pnm");
string type, maxColor;
int width, height;
if(_file){
_file >> type;
if(type != "P6")
cout << "Error! File type is not allowed." << endl;
_file >> width >> height >> maxColor;
_file.close();
egl_inicializar(width, height, true);
image = new RGB *[height];
for(int row = 0; row < height; row++)
image[row] = new RGB[width];
//Working 8D
//_file.open("..\\bin\\birch.pnm", ios::binary);
_file.open("..\\bin\\checkers.pnm", ios::binary);
//Not working D:<
//_file.open("..\\bin\\cathedral.pnm", ios::binary);
//_file.open("..\\bin\\fish_tile.pnm", ios::binary);
//_file.open("..\\bin\\cotton.pnm", ios::binary);
//imagem img; img.carregar("..\\bin\\birch.pnm");
_file.seekg(0, _file.end);
int size = _file.tellg();
int currentSize = 0, counter = 0;
char byte;
_file.seekg(0, _file.beg);
do{
_file.read(reinterpret_cast<char *> (&byte), sizeof(char));
if(byte == 10 || byte == 13)
counter++;
}while(counter < 3);
int rows = 0, columns = 0;
while(size != currentSize){
_file.read(reinterpret_cast<char *> (&pixel), sizeof(RGB));
if(rows < height && columns < width){
image[rows][columns] = pixel;
rows++;
}
else if(rows == height){
rows = 0;
columns++;
image[rows][columns] = pixel;
rows++;
}
//else if(columns >= width)
//currentSize = size;
currentSize = _file.tellg();
}
_file.close();
while(!key[SDLK_ESCAPE]){
for(int row = 0; row < height; row++)
for(int column = 0; column < width; column++)
//egl_pixel(row, column, image[row][column].red, image[row][column].green, image[row][column].blue);
egl_pixel(column, row, image[column][row].red, image[column][row].green, image[column][row].blue);
//img.desenha(0, 0);
egl_desenha_frame(false);
}
}
egl_finalizar();
return 0;
}
It doesn't make sense, as it works for two of them, should work form them all
I opened them all in a text editor and they have the header, so the problem is not there. What am I doing wrong? My colleague wrote a code that stores the pixels into an array with size [height * width] and can read almost all of the images but cathedral.pnm.
Thanks for the patience and help :)

Answer 1

The specs for the pnm state that the values in the header are separated by whitespace, usually newlines, but they could also be spaces or tabs (or something else I can't think of at the moment ;). The cathedral file for instance has a space as separator.
And you're reading the files top to bottom, left to right, in stead of left to right, top to bottom, as per the specs.
And if you want to be really correct, if maxColor is not less than 256, you should read shorts in stead of chars.
You can find the specs here by the way:
http://netpbm.sourceforge.net/doc/ppm.html
Good luck!