这个人是如何用 Microsoft Paint 编写“ Hello World”代码的？

我只是在过去的几天看到了这一点，不能弄清楚它是如何工作的。我谈论的视频是 给你:

它是这个堆栈溢出问题中的 收视率最高的答案: 为什么这个程序被三个编译器拒绝了？

这个位图是如何显示“ Hello World”的 C + + 程序的？

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I assume you're referring to the answer to one of the April Fools questions.

My guess is that each pixel has a binary representation for it. And that each character in source code has a binary representation for it.

The person who created the program must have worked out the color for each pixel that'd have a binary representation that'd correspond to each character.

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A BMP (DIB) image is composed by a header followed by uncompressed1 color data (for 24 bpp images it's 3 bytes per pixel, stored in reverse row order and with 4 bytes row stride).

The bytes for color data are used to represent colors (i.e. none of them are "mandated" by the file format2, they all come from the color of each pixel), and there's a perfect 1:1 correspondence between pixel colors and bytes written in the file; thus, using perfectly chosen colors you can actually write anything you want in the file (with the exception of the header).

When you open the generated file in notepad, the color data will be shown as text; you can still clearly see from the header (the part from BM to the start of the text), that is mandated by the file format.

In my opinion this video was done this way: first the author calculated the size needed for the bitmap, and created a DIB file of the correct size filled with a color that expands to a simple pattern (e.g. all bytes 65 => 'A'); then replaced such pattern with the "payload" code, as shown in the video.

Notice however that it's not impossible to hand-craft the whole thing with notepad - with the color chooser dialog, an ASCII table and a basic knowledge of the DIB format it can be done, but it would be much much slower and error-prone.

More info about the DIB format

  1. There are RLE compressed DIBs, but in this case uncompressed bitmaps are used (and they are used really rarely anyway).
  2. With the exception of the stride, that was avoided using rows multiple of 4 bytes.
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From a theoretical computer science point of view, it would be interesting to ask, if every program can be written in such a way so that, viewed as a bitmap, you actually saw the source code that does the same thing. If you are seriously interested in such results, read e.g. about the Kleene's fixed point theorem.

Program-as-an-image can also be viewed as a form of code obfuscation. Not that it were particularly practical...


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