- 声明时变量的默认值 -

发布于 2024-08-29 00:17:59 字数 517 浏览 7 评论 0原文

我想知道在初始化变量之前它们的默认值是什么...

例如，如果我这样做：

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

这里还有更多例子：

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { // TRUE or FALSE ?

// do whatever

}

更一般地说，当我这样做时返回什么：

[myObjectOnlyDeclaredAndNotInitialized myCustomFunction];

谢谢您的回答。

戈蒂耶。

原文

I was wondering what were the default values of variables before I initialized them...

For example, if I do :

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

Some more examples here :

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { // TRUE or FALSE ?

// do whatever

}

More generally, what is returned when I do :

[myObjectOnlyDeclaredAndNotInitialized myCustomFunction];

Thank you for your answers.

Gotye.

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玩物 2024-09-05 00:17:59

答案是，这取决于变量定义的范围。

Objective-C 对象的实例变量总是初始化为 0/nil/false，因为分配的内存被清零。

全局变量可能初始化为0/nil/false，因为当内存首次分配给进程时，它也会被操作系统清零。然而，当然，我从不依赖它，并且总是自己初始化它们。

局部变量未初始化，并且将包含随机数据，具体取决于堆栈的增长/收缩方式。

注意，对于指向 Objective-C 对象的指针，您可以安全地将消息发送到 nil。因此，例如：

NSArray* foo = nil;
NSLog(@"%@ count = %d", foo, [foo count]);

是完全合法的，并且运行时不会崩溃，输出如下：

2010-04-14 11:54:15.226 foo[17980:a0f] (null) count = 0

The answer is that it depends on the scope in which the variable is defined.

Instance variables of Objective-C objects are always initialised to 0/nil/false because the memory allocated is zeroed.

Global variables are probably initialised to 0/nil/false to because when memory is first allocated to a process, it is also zeroed by the operating system. However, as a matter of course, I never rely on that and always initialise them myself.

Local variables are uninitialised and will contain random data depending on how the stack has grown/shrunk.

NB for pointers to Objective-C objects, you can safely send messages to nil. So, for instance:

NSArray* foo = nil;
NSLog(@"%@ count = %d", foo, [foo count]);

is perfectly legal and will run without crashing with output something like:

2010-04-14 11:54:15.226 foo[17980:a0f] (null) count = 0

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离旧人 2024-09-05 00:17:59

默认情况下 NSArray 值将为 nil ，如果你不初始化它。

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趴在窗边数星星i 2024-09-05 00:17:59

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

Bool myBool 如果未初始化将收到默认值 False。

NSArray *myArray 如果未分配，初始化（例如 NSArray *myArray = [[NSArray alloc] init];）将具有默认值 NIL。如果你对一个统一的数组调用 count ，你将收到一个非 0 的异常。

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { => here it should crash because of [myArray count]

// do whatever

}

对于 NSUInteger myInteger ，默认值应该是 0，文档说这是用来描述一个无符号整数（我没有；虽然这个整数不代表整数））

当您调用 [myObjectOnlyDeclaredAndNotInitialized myCustomFunction]; 时，它应该中断，抛出异常。

希望有帮助

//myClass.h

BOOL myBOOL; // default value ?
NSArray *myArray; // default value ?
NSUInteger myInteger; // default value ?

the Bool myBool if not initialized will receive the default value of False.

NSArray *myArray if not allocated,initialized(for example NSArray *myArray = [[NSArray alloc] init];) will have the default value of NIL. if you call count on an unitialized array you will receive an exception not 0.

//myClass.m
// myArray is not initialized, only declared in .h file

if ([myArray count] == 0) { => here it should crash because of [myArray count]

// do whatever

}

for the NSUInteger myInteger the default value should be 0, the documentation says that this is used to describe an unsigned integer(i didn;t represent integers with this one though)

when you call [myObjectOnlyDeclaredAndNotInitialized myCustomFunction]; it should break, throw an exception.

hope it helps

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