C++ 指向布尔值的指针
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C++ pointer to boolean value
提问by user2737492
I'm having problems trying to implement a class which contains a pointer to a boolean...
我在尝试实现一个包含指向布尔值的指针的类时遇到问题...
class BoolHolder {
public:
BoolHolder(bool* _state);
bool* state;
}
BoolHolder::BoolHolder(bool* _state) {
state = _state;
}
bool testbool = false;
BoolHolder testbool_holder( &testbool );
If I do this, testbool_holder.state always reports that it is true, no matter whether testbool itself is true or false
如果我这样做，testbool_holder.state 总是报告它是真的，不管 testbool 本身是真还是假
What am I doing wrong? I just want the class to be able to maintain an up to date value for testbool but I don't know how to effect this. Thanks
我究竟做错了什么？我只是希望该类能够为 testbool 维护一个最新的值，但我不知道如何实现这一点。谢谢
回答by Neil Kirk
testbool_holder.statereturns true if state is not a null pointer
testbool_holder.state如果 state 不是空指针，则返回 true
*(testbool_holder.state)returns the value of the bool pointed to by state
*(testbool_holder.state)返回状态指向的布尔值
Try this for a more C++ solution
试试这个以获得更多的 C++ 解决方案
class BoolHolder
{
public:
BoolHolder(bool* state) : state(state) {}
bool GetState() const { return *state; } // read only
bool& GetState() { return *state; } // read/write
private:
bool* state;
}
bool testbool = false;
BoolHolder testbool_holder(&testbool);
if (testbool_holder.GetState()) { .. }
Remove the second getter if you only want to allow read access (and maybe change the pointer to const bool *) If you want both, then you need both getters. (This is because read/write can't be used to read on a const object).
如果您只想允许读取访问（并且可能将指针更改为const bool *），请删除第二个 getter如果您想要两者，那么您需要两个 getter。（这是因为读/写不能用于读取 const 对象）。
回答by Hrishi
It's right. What you have is not the value of the boolean but a pointer to the boolean. You must dereference the pointer to obtain the value of the bool itself. Since you have a pointer, it will contain an address which is an integer. Since in C and C++ all non zero integers are true, you will get true.
这是正确的。您拥有的不是布尔值，而是指向布尔值的指针。您必须取消引用指针才能获得 bool 本身的值。由于您有一个指针，它将包含一个整数地址。因为在 C 和 C++ 中所有非零整数都是真的，你会得到真的。
