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[ISSUE #71]Fixed the issue that dangling reference returned when getting message property . #73

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Jan 22, 2019
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[ISSUE #71]Fixed the issue that dangling reference returned when getting message property . #73

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9 changes: 6 additions & 3 deletions src/message/MQMessage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,9 @@ const string MQMessage::PROPERTY_TRANSACTION_CHECK_TIMES = "TRANSACTION_CHECK_TI
const string MQMessage::PROPERTY_CHECK_IMMUNITY_TIME_IN_SECONDS = "CHECK_IMMUNITY_TIME_IN_SECONDS";

const string MQMessage::KEY_SEPARATOR = " ";

static const string EMPTY_STRING = "";
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@jovany-wang jovany-wang Jan 21, 2019 •
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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.

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@ifplusor ifplusor Jan 21, 2019

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@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.

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@jovany-wang jovany-wang Jan 21, 2019

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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.:)

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@ifplusor ifplusor Jan 21, 2019

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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.

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@jovany-wang jovany-wang Jan 21, 2019

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@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.

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@ifplusor ifplusor Jan 21, 2019

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


//<!************************************************************************
MQMessage::MQMessage() { Init("", "", "", 0, "", true); }

Expand Down Expand Up @@ -109,9 +112,9 @@ void MQMessage::setPropertyInternal(const string& name, const string& value) {

const string & MQMessage::getProperty(const string& name) const {
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@jonnxu jonnxu Jan 21, 2019

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@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

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@ifplusor ifplusor Jan 21, 2019

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@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.

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@jovany-wang jovany-wang Jan 21, 2019

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

map<string, string>::const_iterator it = m_properties.find(name);
if(it == m_properties.end()){
return "";
}else{
if (it == m_properties.end()) {
return EMPTY_STRING;
} else {
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@jovany-wang jovany-wang Jan 21, 2019

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nice catch for the code style.

return it->second;
}
}
Expand Down