How to convert uint32 to string?

I would simply use Sprintf or even just Sprint:

var n uint32 = 42
str := fmt.Sprint(n)
println(str)

Go is strongly typed. Casting a number directly to a string would not make sense. Think about C where string are char * which is a pointer to the first letter of the string terminated by \0. Casting a number to a string would result in having the first letter pointer to the address of the number, which does not make sense. This is why you need to "actively" convert.

I would do this using strconv.FormatUint:

import "strconv"

var u uint32 = 17
var s = strconv.FormatUint(uint64(u), 10)
// "17"

Note that the expected parameter is uint64, so you have to cast your uint32 first. There is no specific FormatUint32 function.

For a more robust solution, you can use text/template:

package main

import (
   "text/template"
   "strings"
)

func format(s string, v interface{}) string {
   t, b := new(template.Template), new(strings.Builder)
   template.Must(t.Parse(s)).Execute(b, v)
   return b.String()
}

func main() {
   imap := struct{UID uint32}{999}
   s := format("{{.UID}}", imap)
   println(s == "999")
}

https://pkg.go.dev/text/template

To summarize:

strconv.Itoa doesn't seem to work

strconv.Itoa accepts int, which is signed integer (either 32 or 64 bit), architecture-dependent type (see Numeric types).

I need to convert an uint32 to string

1. Use fmt.Sprint
2. Use strconv.FormatUint

The better option is strconv.FormatUint because it is faster, has less memory allocations (benchmark examples here or here).

A cast string(t) could have been so much easier.

Using string does not work as some people expect, see spec:

Converting a signed or unsigned integer value to a string type yields a string containing the UTF-8 representation of the integer. Values outside the range of valid Unicode code points are converted to "\uFFFD".

This function is going to be removed from Go2, see Rob Pike's proposal