Where I can find a url decode algorithm

[wingleader]

Hi everybody!

I have such a problem. I wrote a web portal on C++, but I found one big "-" in that script: C++ is not supporting url decoding(I mean data sent by HMTL forms).

As a developer I can solve this problem in many ways, but the easier would be, if I understand how to convert ASCII Hex (%D3 for example) to a symbol it represents.

As I guess, there must be a certain algorythm how it was encoded, and the same how it may be decoded.
As we all know there is a certain way to convert digits to binary(I mean if you have 57 for example, then:
32 16 8 4 2 1
57/32= 1 , 25/16=1, 9/8=1 , 1/4 = 0, 1/2 = 0 , 1/1 = 1, so binary is 111001.
Is there some kind of formula to convert ASCII Hex to ASCII, or easier to say how to decode URL content?
Thanks to everyone.

[Ganon11]

If I understand it correctly, a hex number in HTML with the form %XY is a character encoded in Hexidecimal, with number value XY. To find the ASCII version, you should only have to convert to decimal. The value (in decimal) of a hex number XY is X * 16 + Y.

So, when parsing the imformation, you can look for a '%' symbol. If you find one, you have come across a hex character that needs to be decoded. Discard the '%' and retrieve the XY numbver, convert to decimal using the above formula, and then cast it to a character in order to decode.

[wingleader]

Pardon, I've been mistaken... It's a little bit different, first comes numder, then a char: %3A%3D%5B%5D.

each char is represented is 3 chars.

so, if i need to convert %3A to char, I need to 3x16 + A?

And the last question: how I convert decimal to char?
http://spacelogic.eu/cgi-bin/spacelogic.cgi - here is a link to script. I'm sorry it's in russian, but it works the same way.

[Ganon11]

OK, the process still holds. Remember, in hexidecimal, a letter is basically a digit. So all you have to do is get each digit individually - if a digit is a number (0-9), you can multiple normally. If it's a letter (A-F), convert it to its equivalent (A = 10, B = 11, etc), and then proceed with the multiplication.

As for the decimal number to a character, just make a char variable and initialize it to a number:

char myChar = 90;

[wingleader]

Thanks a lot! It works fine. A REALLY HUGE THANKS!!!

[wingleader]

By the way, do you know how russian symbols are represented in ASCII?
Somehow they all have negative values(in HEX it's %E0 and in ASCII it's -48).

PS. I found an answer. All russian symbols comes over 127 limit, and as a result, char value comes as: 127 - font_value, and here comes "-" symbol.

So huge thanks for help! I even did't hope to get answers so quickly.