如何测试Objective-C中的基元是否为零？ [英] How do I test if a primitive in Objective-C is nil?

问题描述

我正在检查iPhone应用程序 -

I'm doing a check in an iPhone application -

int var;
if (var != nil)

它有效，但在X-Code中这是生成警告指针和整数之间的比较。我如何解决它？

It works, but in X-Code this is generating a warning "comparison between pointer and integer." How do I fix it?

我来自Java世界，在那里我很确定上述陈述会因为赞美而失败。

I come from the Java world, where I'm pretty sure the above statement would fail on compliation.

推荐答案

原语不能 nil 。 nil 保留用于指向Objective-C对象的指针。 nil 在技术上是指针类型，混合指针和整数将没有强制转换将几乎总是导致编译器警告，但有一个例外：完全可以隐式转换整数0到没有强制转换的指针。

Primitives can't be nil. nil is reserved for pointers to Objective-C objects. nil is technically a pointer type, and mixing pointers and integers will without a cast will almost always result in a compiler warning, with one exception: it's perfectly ok to implicitly convert the integer 0 to a pointer without a cast.

如果要区分0和无值，请使用 NSNumber class：

If you want to distinguish between 0 and "no value", use the NSNumber class:

NSNumber *num = [NSNumber numberWithInt:0];
if(num == nil)  // compare against nil
    ;  // do one thing
else if([num intValue] == 0)  // compare against 0
    ;  // do another thing

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