How to convert a UUID that saved in an array of bytes into a string (c++)

Question

I have a UUID that saved as a 16 byte data like this:

   unsigned char uuid[16]; //128-bits unique identifier

and I want to convert it to a std::string. I can probably write a loop to go thought all bytes and generate the string, but I am looking for a simpler/faster solution. Is there any such solution?

Answer 1

If you really want to avoid a loop, you can always do something like:

char str[37] = {};
sprintf(str, 
"%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x", 
    uuid[0], uuid[1], uuid[2], uuid[3], uuid[4], uuid[5], uuid[6], uuid[7],
    uuid[8], uuid[9], uuid[10], uuid[11], uuid[12], uuid[13], uuid[14], uuid[15]
);

Not really elegant, but i think it's the best you can get without loop and without platform dependency.

Answer 2

Answer on this question is wrong by all means.

According to https://en.wikipedia.org/wiki/Universally_unique_identifier#Format

This is the correct code:

char str[37] = {};
unsigned long data1 = *reinterpret_cast<unsigned long*>(uuid);
unsigned short data2 = *reinterpret_cast<unsigned short*>(uuid + 4);
unsigned short data3 = *reinterpret_cast<unsigned short*>(uuid + 6);
sprintf(str, 
"%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x", 
    data1, data2, data3,
    uuid[8], uuid[9], uuid[10], uuid[11], uuid[12], uuid[13], uuid[14], uuid[15]
);

Answer 3

Write a loop. For each byte, snprintf of %#02x. Do not forget the conventional dashes.

There is no platform-independent (ie POSIX) API that formats UUIDs, so this is the best you are going to get.

Answer 4

basic_string supplys this constructor:

basic_string(const E *s, size_type n, const A& al = A());

So you can do it like this:

string strUuid(uuid, 16);