如何测试Objective-C中的基元是否为零？

I'm doing a check in an iPhone application -

我正在检查iPhone应用程序 -

int var;
if (var != nil)

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

它可以工作，但在X-Code中，这会产生一个警告“指针和整数之间的比较”。我如何解决它？

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

我来自Java世界，在那里我很确定上面的陈述会因为赞美而失败。

2 个解决方案

#1

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.

基元不能为零。 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：完全可以将整数0隐式转换为没有强制转换的指针。

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

如果要区分0和“无值”，请使用NSNumber类：

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

#2

if (var) {
    ...
}

Welcome to the wonderful world of C. Any value not equal to the integer 0 or a null pointer is true.

欢迎来到C的精彩世界。任何不等于整数0或空指针的值都是真的。

But you have a bug: ints cannot be null. They're value types just like in Java.

但你有一个bug：int不能为null。它们就像在Java中一样是值类型。

If you want to "box" the integer, then you need to ask it for its address:

如果你想“整理”整数，那么你需要询问它的地址：

int can_never_be_null = 42; // int in Java
int *can_be_null = &can_never_be_null; // Integer in Java
*can_be_null = 0; // Integer.set or whatever
can_be_null = 0;  // This is setting "the box" to null,
                  //  NOT setting the integer value

#1