C++ How to get the Image size of a png file (in directory)

Question

Is there a way of getting the dimensions of a png file in a specific path? I don´t need to load the file, I just need the width and height to load a texture in directx.

(And I don´t want to use any third-party-libs)

Answer 1

The width is a 4-byte integer starting at offset 16 in the file. The height is another 4-byte integer starting at offset 20. They're both in network order, so you need to convert to host order to interpret them correctly.

#include <fstream>
#include <iostream>
#include <winsock.h>

int main(int argc, char **argv) { 
    std::ifstream in(argv[1]);
    unsigned int width, height;

    in.seekg(16);
    in.read((char *)&width, 4);
    in.read((char *)&height, 4);

    width = ntohl(width);
    height = ntohl(height);

    std::cout << argv[1] << " is " << width << " pixels wide and " << height << " pixels high.\n";
    return 0;
}

As-is, this is for windows. For Linux (or *bsd, etc.) you'll need to #include <arpa/inet.h> instead of <winsock.h>.