Qt String Comparison

Question

Suppose I have:

QString x;

Is the following code fragment:

if(x.compare("abcdefg") == 0){
  doSomething();
}
else{
  doSomethingElse();
}

... functionally equivalent to:

if(x == "abcdefg"){
  doSomething();
}
else{
  doSomethingElse();
}

I could prove this for myself by writing a fairly trivial program and executing it, but I was surprised I couldn't find the question / answer here, so I thought I'd ask it for the sake of future me / others.

That's fine, but what has the QVariant got to do with anything? You're operating on a QString instance, the fact that you got it from QVariant is quite immaterial here because you obtain it the same way in both cases. It doesn't even matter that canConvert<QString> returns true. You'll get valid results when it returns false, too. Besides, why do you care what compare returns? You want to compare strings, use the operator==, it's what it's for. — Kuba hasn't forgotten Monica
– Kuba hasn't forgotten Monica, Commented Sep 9, 2016 at 18:33
@KubaOber you're right, I've removed the QVariant distractions — vicatcu
– vicatcu, Commented Sep 9, 2016 at 20:11

Community · Accepted Answer · 2017-05-23 12:08:23Z

3

QString::compare will only return zero if the string passed to it and the string it is called on are equal.

Qstring::operator== returns true if the strings are equal otherwise, false.

Since compare only returns zero when the strings are equal then

(qstrign_variable.compare("text") == 0) == (qstrign_variable == "text")

If qstrign_variable contains "text" in the above example. If qstrign_variable contains something else then both cases evaluate to false.

Also note that std::string has the same behavior

edited May 23, 2017 at 12:08

CommunityBot

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answered Sep 9, 2016 at 17:44

NathanOliver

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