C function to encode a Unicode code point as UTF-8 byte array

utf8_encode.c

#include <stdint.h>

/**
 * Encode a code point using UTF-8
 * 
 * @author Ondřej Hruška <ondra@ondrovo.com>
 * @license MIT
 * 
 * @param out - output buffer (min 5 characters), will be 0-terminated
 * @param utf - code point 0-0x10FFFF
 * @return number of bytes on success, 0 on failure (also produces U+FFFD, which uses 3 bytes)
 */
int utf8_encode(char *out, uint32_t utf)
{
  if (utf <= 0x7F) {
    // Plain ASCII
    out[0] = (char) utf;
    out[1] = 0;
    return 1;
  }
  else if (utf <= 0x07FF) {
    // 2-byte unicode
    out[0] = (char) (((utf >> 6) & 0x1F) | 0xC0);
    out[1] = (char) (((utf >> 0) & 0x3F) | 0x80);
    out[2] = 0;
    return 2;
  }
  else if (utf <= 0xFFFF) {
    // 3-byte unicode
    out[0] = (char) (((utf >> 12) & 0x0F) | 0xE0);
    out[1] = (char) (((utf >>  6) & 0x3F) | 0x80);
    out[2] = (char) (((utf >>  0) & 0x3F) | 0x80);
    out[3] = 0;
    return 3;
  }
  else if (utf <= 0x10FFFF) {
    // 4-byte unicode
    out[0] = (char) (((utf >> 18) & 0x07) | 0xF0);
    out[1] = (char) (((utf >> 12) & 0x3F) | 0x80);
    out[2] = (char) (((utf >>  6) & 0x3F) | 0x80);
    out[3] = (char) (((utf >>  0) & 0x3F) | 0x80);
    out[4] = 0;
    return 4;
  }
  else { 
    // error - use replacement character
    out[0] = (char) 0xEF;  
    out[1] = (char) 0xBF;
    out[2] = (char) 0xBD;
    out[3] = 0;
    return 0;
  }
}

undefined reference to WinMain

How to fix it?
Say pls

I have no idea what you're talking about, there's no WinMain in my code

its error

and this code not working(

The code is correct, you have something broken in the rest of your program. Try asking on https://stackoverflow.com/

alredy

are you using linux?

Please stop posting to this gist, it is NOT related to the error you're getting and I don't have the time or the will to troubleshoot your program. StackOverflow is the place to get help.

Eugenetucha are you assuming this snippet is a standalone program? You need to provide your own main() or WinMain() that uses it, or compile it as library or linkable object.

how to convet a double to UTF-8 bytes?

@wangjunfeng90214 what do you mean by double?

@MightyPork just wanted to say thanks, due to this i dont have to rely on the icu library! <3