In other languages, such as Go, there are a myriad of libraries that can be used to create a globally unique ID string (using elements such as nanosecond time, machine id, process id, random bytes...)

However, in C , the only real choice seems to be UUID (such as that from Boost)

I am looking to use a globally unique identifier in my code, but do not want something with as many chars as a UUID.

As an example of the type of things available in GoLang. Please see the below. Anything similiar in c ?

https://blog.kowalczyk.info/article/JyRZ/generating-good-unique-ids-in-go.html

CodePudding user response：

Please note that when I say "as many chars", I am referring to the string representation of a UUID

So, perhaps use your own representation.

You didn't specify a whole lot. Keep in mind that time-clustering might lead to security vulnerabilities¹. I'd assume UUIDv4 standard, meaning 16 bytes. Let's use the encoding from the linked page that looks shortish:

Live On Coliru

#include <boost/lexical_cast.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <cstring>
#include <iostream>
#include <string_view>

using boost::uuids::uuid;
static_assert(uuid::static_size() == 16);

static constexpr auto alphabet57 =
    "23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

std::string encode57(uuid uid) {
    boost::uint128_type num;
    std::reverse(uid.data, uid.data 16);
    std::memcpy(&num, uid.data, 16);

    std::string s;
    s.reserve(12);

    while (num) {
        s  = alphabet57[num % 57];
        num /= 57;
    }

    return s;
}

uuid decode57(std::string_view s) {
    boost::uint128_type num = 0;

    for (auto it = s.rbegin(); it != s.rend();   it) {
        num *= 57;
        num  = std::find(alphabet57, alphabet57   57, *it) - alphabet57;
    }

    uuid uid;
    std::memcpy(uid.data, &num, 16);
    std::reverse(uid.data, uid.data   16);

    return uid;
}

int main() {
    for (std::string test : {
             "f7dd5274-f457-4239-a881-801662d589ad", // sfitJnfge8vaXnga8kzi7n
             "3b387615-24ed-4c17-a715-c4413ffac3b5", // Vq6uZe6usvSwWftVdBPbYC
             "3dd64dba-1ff3-40e5-84e3-3fbb0f8b86b9", // r5D3drtfrx7322ajzYv82D
             "b17a848e-5d6b-45d9-ae25-57cfb8a8fec3", // petYHah9W3p8GptQ9QJuaZ
             "a9edc682-147c-4e41-85e2-e06c4ce64086", // DFLa6tquGSZvSEi2WE3MFY
             "2cc90c4a-192f-4b57-bc11-2c322dab2ce0", // yyg6AekktrpjdBCjGjsCy9
             "ac1d94bd-3fbc-46c1-aeec-cdcdc2dd0dd2", // dzHCNTADG6R4n3QTjm7XdY
             "1e3df271-a3c2-4b45-8871-0fde4c2d97e8", // tL66L6gqRESaABWsxbrhP7
             "0d15c1d5-3646-474f-8a5d-989878f12a95", // FtnvH2QRENpsFcLXq5zhL4
             "ececc5dc-cdf1-49f4-b3f7-bfe8697133fd", // Dkfm7JmgVAuP28JLPDBnAk
         })                                          //
    {
        auto const uid = boost::lexical_cast<uuid>(test);
        auto const txt = encode57(uid);
        std::cout << uid << " ~ " << txt << "\n";
        assert(decode57(txt) == uid);
    }
}

Prints

f7dd5274-f457-4239-a881-801662d589ad ~ sfitJnfge8vaXnga8kzi7n
3b387615-24ed-4c17-a715-c4413ffac3b5 ~ Vq6uZe6usvSwWftVdBPbYC
3dd64dba-1ff3-40e5-84e3-3fbb0f8b86b9 ~ r5D3drtfrx7322ajzYv82D
b17a848e-5d6b-45d9-ae25-57cfb8a8fec3 ~ petYHah9W3p8GptQ9QJuaZ
a9edc682-147c-4e41-85e2-e06c4ce64086 ~ DFLa6tquGSZvSEi2WE3MFY
2cc90c4a-192f-4b57-bc11-2c322dab2ce0 ~ yyg6AekktrpjdBCjGjsCy9
ac1d94bd-3fbc-46c1-aeec-cdcdc2dd0dd2 ~ dzHCNTADG6R4n3QTjm7XdY
1e3df271-a3c2-4b45-8871-0fde4c2d97e8 ~ tL66L6gqRESaABWsxbrhP7
0d15c1d5-3646-474f-8a5d-989878f12a95 ~ FtnvH2QRENpsFcLXq5zhL4
ececc5dc-cdf1-49f4-b3f7-bfe8697133fd ~ Dkfm7JmgVAuP28JLPDBnAk

¹ these all are examples of RFC4122 random-number based UUIDs, the default when using goolge/uuid in Go

These encodings have been verified with the ones generated by shortuuid