如何比较字符串？ （`==` 返回错误值）

Question

I've got myself a piece of the iPhone SDK and been trying to make some simple apps. In this one, i want to compare the first character of self.label.string with the last one of ((UITextField *)sender).text . I decided to name them self.texty and self.input , respectively.

I would expect this if statement returning yes to me under certain circumstances, however I can't seem to get that done.

(in my case, my self.label.string was equal to 'hello,', while my self.input ended in an 'h'.)

self.input = [NSString stringWithFormat:@"%@", [((UITextField *)sender).text substringFromIndex:[((UITextField *)sender).text length]-1]];
self.texty = [NSString stringWithFormat:@"%@", [self.label.string substringToIndex:1]];

if (self.input == self.texty) {
    return yes;
} else {
    return no;
}

Answer 1

String comparison is not done with == , but with one of the comparison methods of NSString .

For example:

if ([self.input compare:self.texty] == NSOrderedSame) {

Answer 2

if ([self.input isEqualToString:texty]) {
    return yes;
} else {
    return no;
}

EDIT:

Or a better version as the commenters noted:

return [self.input isEqualToString:texty];

Answer 3

If you're curious why the == operator doesn't work as expected, it's because you're actually comparing two scalar types (pointers to NSString objects) not the contents of the NSString objects themselves. As a result, it will return false unless the two compared NSStrings are actually the same instance in memory, regardless of the contents.