Picture.pbm --> decimal, in c++ - c++

Question

just want to ask if anyone knows why I cant convert an entire picture into decimal.
Problem: after about 180 couts it turns 0 for the rest of the pixels.
Code:
#include <fstream>
#include <iostream>
int main() {
char unsigned charTemp = 0;
int unsigned intTemp = 0;
std::fstream file;
file.open("PIC.pbm", std::ios::in);
//Ignore header
for (int i = 0; i < 13; i++) {
file.ignore();
}
//read and print
//img res is 40x40 = 1600
for (int i = 0; i < 1600; i++) {
file >> charTemp;
intTemp = charTemp;
std::cout << intTemp << " ";
charTemp = 0;
intTemp = 0;
}
std::cout << "\n\n\n";
system("pause");
return 0;
}
Pic: any 40x40 pbm

Answer 1

A better method with picture and image files is to read them as binary files:
std::ifstream file("PIC.pbm", ios::binary);
std::vector<unsigned char> bitmap(1600);
// Skip over the header
file.seekg(13, ios::beg); // Skip over 13 bytes.
// Read in the data at once
file.read((char *) &bitmap[0], 1600);
// Now process the bitmap from memory
for (int i = 0; i < 1600; ++i)
{
cout << static_cast<unsigned int>(bitmap[i]) << " ";
if ((i % 40) == 39)
{
cout << "\n";
}
}
cout << "\n";
The idea here is to read in the bitmap in one transaction into memory. Streams like to flow (don't interrupt the flow). Memory is faster to access than files, so the bitmap values are processed from memory.
The cast is used so that the formatted insertion doesn't treat the byte as a character, but a number.

Answer 2

First, open your PIC.pbm file in another hex editor because it's quite possible that those bytes really are zeroes. If not, then you've got problems reading the file.
The fstream constructor does not default to reading in binary mode, so it reads files as "text" - and I've learned the hard way that you can't trust the standard-library with knowing anything about text anymore (what with mishandling Unicode, line-endings, etc - I feel it's best to always use binary and a dedicated Unicode library).
You should check the fstream::good() function after each read operation to see if it failed, and if so, then check iostate:
using namespace std;
// ...
fstream file;
file.open( "PIC.pbm", ios::in | ios::binary );
file.ignore( 13 );
for (int i = 0; i < 1600; i++) {
file >> charTemp;
if( !file.good() ) {
cout << endl;
cout << "Error reading file: iostate == " << file.iostate << endl;
break;
}
else {
intTemp = charTemp;
std::cout << intTemp << " ";
charTemp = 0;
intTemp = 0;
}
}