Question

In my C++ program I want to convert a std:string like this:

abc €

to an UTF-8 escape sequence:

abc%20%E2%82%AC

And I need it to be platform independent! All I found has been solutions only working on windows. There must be a solution out there right?

Answer 1

Prior to C++11, there’s no mandated support for UTF-8 in the standard.

There are two steps here:

• convert to UTF-8 (unless it’s already in UTF-8)
• URL-escape the result (update: James Kanze covers this part)

Neither of them is particularly difficult to write for yourself portably, assuming you know what character encoding the input string uses[*]. Which means other people have done it before, you shouldn’t need to write it yourself. If you search for them separately you might have better luck finding platform-independent code for each step.

Note there are two different ways to URL-escape a space character, either as + or as %20. Your example uses %20, so if that’s important to you then don’t accidentally use a URL-escape routine that does the other.

[*] It’s not ISO-Latin-1, since that doesn’t have the Euro sign[**], but it might be Windows CP-1252.

[**] Unless it’s been added recently. Anyway, your example codes the Euro sign as UTF-8 bytes 0xE2 0x82 0xAC, which represent the Unicode code point 0x20AC, not code point 0x80 which it has in CP1252. So if it was originally a single-byte encoding then clearly an intelligent single-byte-to-unicode-code-point conversion has been applied along the way. You could say there are three steps:

• convert the std::string to Unicode code points (depends on input encoding).
• convert the Unicode to UTF-8
• URL-escape the UTF-8