如何使用UTF-8字符串检查golang中的字符值？

I'm attempting to check if the first character in a string matches the following, note the UTF-8 quote characters:

c := t.Content[0]
if c != '.' && c != ',' && c != '?' && c != '“' && c != '”'{

This code does not work due to the special characters in the last two checks.

What is the correct way to do this?

Indexing a string indexes its bytes (in UTF-8 encoding - this is how Go stores strings in memory), but you want to test the first character.

So you should get the first rune and not the first byte. For efficiency you may use utf8.DecodeRuneInString() which only decodes the first rune. If you need all the runes of the string, you may use type conversion like all := []rune("I'm a string").

See this example:

for _, s := range []string{"asdf", ".asdf", "”asdf"} {
    c, _ := utf8.DecodeRuneInString(s)
    if c != '.' && c != ',' && c != '?' && c != '“' && c != '”' {
        fmt.Println("Ok:", s)
    } else {
        fmt.Println("Not ok:", s)
    }
}

Output (try it on the Go Playground):

Ok: asdf
Not ok: .asdf
Not ok: ”asdf

Adding to @icza's great answer: It's worth noting that while indexing of strings is in bytes, range of strings is in runes. So the following also works:

for _, s := range []string{"asdf", ".asdf", "”asdf"} {
    for _, c := range s {
        if c != '.' && c != ',' && c != '?' && c != '“' && c != '”' {
            fmt.Println("Ok:", s)
        } else {
            fmt.Println("Not ok:", s)
        }
        break // we break after the first character regardless
    }
}