Objective-C:调试器中的实例变量超出范围 [英] Objective-C: instance variables out of scope in debugger

问题描述

我有一个超类和一个子类，它们都定义了实例变量.

I have a superclass and a subclass, both of which define instance variables.

超类的粗略概述:

/* GenericClass.h */
@interface GenericClass : NSObject {
    /* some variables */
}
@end
/* GenericClass.m */
@implementation GenericClass
    /* ... */
@end

子类概述:

/* SpecificClass.h */
#import "GenericClass.h"
@interface SpecificClass : GenericClass {
    NSMutableString *str;
}
/* SpecificClass.m */
#import "SpecificClass.h"
@implementation SpecificClass
- (void)aMethod {
    //Debugger reports str as out of scope
    str = [[NSMutableString alloc] initWithCapacity:100];
    //Works fine:
    self->str = [[NSMutableString alloc] initWithCapacity:100];
    //Doesn't compile as I haven't defined @property/@synthesize:
    self.str = [[NSMutableString alloc] initWithCapacity:100];
}

当我使用直接从 NSObject 继承的类时，不需要 self-> 指针.请注意，在父 GenericClass 中没有定义名称为 str 的对象.所以，我的问题是，当没有被引用为 self->str 时，为什么 str 超出了范围?代码本身有效，但我无法使用调试器读取变量

When I am using classes that inherit directly from NSObject, one doesn't need the self-> pointer. Note that there is no object with the name str defined in the parent GenericClass. So, my question is, why is str out of scope when not referenced as self->str? The code in itself works, but I can't read the variable with the debugger

推荐答案

GDB 不是 Objective-C 编译器.编译器知道像 Objective-C 方法中的词法作用域之类的东西，但 GDB 不知道.但是，它确实理解局部变量.

GDB is not an Objective-C compiler. The compiler knows about things like lexical scope within Objective-C methods, but GDB does not. It does, however, understand local variables.

在Objective-C 中，每个方法都有一个隐式的self 参数在调用时传递给它.因此，当您查看 self->str 时，GDB 正在解释它，就像它解释任何其他局部变量评估一样.

In Objective-C, every method has an implicit self parameter passed to it when it's called. So when you look at self->str, GDB is interpreting that like it would interpret any other local variable evaluation.

当您尝试自行评估 str 时，GDB 将查找名为 str 的局部变量，但未找到，则报告它不在范围内.这不是错误；这是预期的行为.

When you try to evaluate str on its own, GDB will look for a local variable called str and, not finding one, reports that it's not in scope. This is not an error; this is the expected behavior.

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