问题比较NSString文字和常量 [英] Issue comparing NSString literal and constant

问题描述

我有一个 NSString ， firstWord ，其值为"First".定义如下:

I have an NSString, firstWord, that has the value of "First". It was defined like this:

NSString *firstWord = [[NSString alloc] init];

firstWord = [textView text];

但是，当我尝试检查其值时，就像这样:

However, when I try to check its value, like so:

if (firstWord == @"First"){}

在Objective-C中，比较未返回true或YES.我知道它确实具有与字符串相同的值.因此，来自这我是我很确定问题是我正在比较指针，尽管字符串本身确实具有相同的值，但这里的指针并不相同.那么，如何直接比较字符串本身呢?或者也许更有效地，确保两个字符串对象 do 具有相同的指针，所以我不必进行相对昂贵的字符串比较吗?

The comparison does not return true, or YES I guess in Objective-C. I know that it does have the same value as a string. So, from this I am pretty sure that the issue is that I am comparing pointers, which are not the same here, even though the strings themselves do have the same value. So how can I directly compare the strings themselves? Or maybe more efficiently, make sure the two string objects do have the same pointer, so I don't have to the do the relatively costly string comparison?

推荐答案

那么如何直接比较字符串本身呢?

So how can I directly compare the strings themselves?

可可中的字符串比较是通过

String comparison in Cocoa is done with isEqualToString:.

或者更有效地，请确保两个字符串对象确实具有相同的指针，

Or maybe more efficiently, make sure the two string objects do have the same pointer,

这是不可能的.一个是字符串文字，存储在应用程序二进制文件的DATA部分中；另一个在应用程序的堆上.在某些情况下(使用 initWithString:@文字字符串" 创建字符串)，您将获得相同的地址，但您不应依赖该地址.

This isn't possible. One is a string literal, stored in the DATA section of your app's binary; the other is on your app's heap. In certain circumstances (creating a string using initWithString:@"literal string") you'll end up with the same address, but you shouldn't rely on that.

顺便说一句，您不必-实际上不应该，因为您正在创建泄漏-在将文本视图的文本分配给指针之前先分配一个字符串.

As an aside, you don't need to -- in fact, shouldn't, because you're creating a leak -- allocate a string before assigning the text view's text to the pointer.

这篇关于问题比较NSString文字和常量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！