打印双重类型struct成员时LLDB中的奇怪行为 [英] Strange behavior in LLDB when printing a double type struct member

问题描述

在某些iOS代码中，我在一个对象上有一个C struct ivar.此结构的成员之一是double类型.如果我在一个方法中分配给该struct成员，则调试程序将在我打印struct本身时(与变量的列表视图一样)报告此struct成员的值的虚假值.直接打印struct成员(p structWithDouble.doubleMember)，我得到正确的值.此外，如果我将此成员的值分配给本地的自动double var，则在列表视图和打印时会看到正确的值.

In some iOS code, I have an C struct ivar on an object. One of the members of this struct is of type double. If I, within a method, assign to this struct member, the debugger reports spurious values for the value of this struct member when I print the struct itself (as does the list view of variables), but when I print the struct member directly, (p structWithDouble.doubleMember), I get the right value. Furthermore, If I assign the value of this member to a local, automatic double var, I see the correct value in the list view and when printing.

我认为这是LLDB的问题，但令人不安和沮丧.这是一个已知的问题?如果是这样，是否有解决方法?

I imagine this is an issue with LLDB, but it's unsettling and frustrating. Is this a known issue? If so, is there a workaround?

typedef struct {
    double doubleMember;
} structWithDouble;

@interface MyClass : NSObject {
    structWithDouble structAsIvar;
}
@end

@implementation

- (void)someMethod {
    structAsIvar.doubleMember = 200.0;
    double localDouble = structAsIvar.doubleMember;
}

在someMethod:内部，调试器变量列表显示以下值:

Inside someMethod:, the debugger variable list shows the following values:

structAsIvar.doubleMember (double) 1.65865e-307
localDouble               (double) 200

在LLDB中，当进入someMethod:时，我得到以下输出:

Over in LLDB, I get the following output when breaking in someMethod::

(lldb) p structAsIvar.doubleMember
(double) $4 = 200

(lldb) p structAsIvar
(structAsIvar) $5 = {
  (double) doublemember = 1.17244e-312
}

(lldb) p localDouble
(double) 200

(lldb) p self->structAsIvar.doubleMember
(double) 200

更新

我发现在使用GDB时，这种行为没有发生.显然LLDB尚未准备好……不过，我仍然对LLDB的解决方法感兴趣.

Update

I've found that none of this behavior happens when using GDB. Apparently LLDB just isn't ready yet... I'm still be interested in a workaround for LLDB, though.

推荐答案

这似乎已在Xcode 4.5的lldb(lldb-167.2)中修复:

It looks like this is fixed in Xcode 4.5's lldb (lldb-167.2):

(lldb)  p structAsIvar.doubleMember
(double) $5 = 200
(lldb)  p structAsIvar
(structWithDouble) $6 = {
  (double) doubleMember = 200
}
(lldb) p localDouble
(double) $7 = 200
(lldb) p self->structAsIvar.doubleMember
(double) $8 = 200
(lldb) 

我不确定哪个版本有此修复程序； Xcode 4.4可能也可以正常工作，但我现在没有手头的东西可以进行测试.

I'm not sure exactly which release had the fix; it's likely Xcode 4.4 also works correctly but I don't have that at hand to test right now.

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