[ISSUE #71]Fixed the issue that dangling reference returned when getting message property .

[ifplusor]

ISSUE #71 ,MQMessage::getProperty return a dangling reference when returning an empty string.

[jonnxu]

@ifplusor hi, if we can change getProperty return string but not string& ? because i don't think there is a need to return reference string for getProperty

[ifplusor]

@jonnxu I think 'const string&' is ok. Here, we need return a read-only object or a new one, and return a reference don't allocate a new object.

[jovany-wang]

I think both of them are fine.
It will not affect efficiency too much.

[jovany-wang]

Thanks, I left a few comments.

[jovany-wang]

nice catch for the code style.

[jovany-wang]

I don't think defining an empty str as a static global var is the best approach.
Maybe we could add a new file constant.h like this:

class Constants {
public:
    static const string EMPTY_STRING = "";
};

Any way, we should avoid to use global variables and global static variables.

[ifplusor]

@jovany-wang the visibility of global static variables is only in this file. i think depend on other file is unnecessary for only this one. if we use EMPTY_STRING in other files, it's ok.

[jovany-wang]

If you don't want to move it to constant.h, let's use return ""; directly?
Because I don't think we should use a global static variable in such case.:)

[ifplusor]

If you don't want to move it to constant.h, let's use return ""; directly?
Because I don't think we should use a global static variable in such case.:)

@jovany-wang now, we return a reference, and return a temp object is a bug.

[jovany-wang]

@ifplusor Thanks, I see.
So if the method may be return a temp variable, it is pretty make sense to declare it as string MQMessage::getProperty(const string& name);.

If the method always return his member variables, we could return a const ref.

[ifplusor]

@jovany-wang i don't change method signature, we can discuss it.

[jovany-wang]

Thanks. Let's merge this PR as a workaround approach first.