CODEWITHSUNDEEP
c++qt
Professor Chaos
Professor Chaos

Reputation: 9060

Passing empty QString by reference

I have a method that has this signature

void SetFoo(QString& foo);

and I'm trying to pass an empty string inline, but none of the following compile 

SetFoo("");
SetFoo(QString(""));

(error: no matching function for call to ‘MyClass::SetFoo(QString)’)

but if I create a variable like this, it works.

QString emptyFoo = "";
SetFoo(emptyFoo);

Is there not a way to call the method without creating a variable explicitly?

NOTE: Everything seem to work in windows environment with using vc++ compiler but I encounter the above mentioned compilation error in linux environment using g++.

Upvotes: 2

Views: 1669

Answers (2)

Karthik T
Karthik T

Reputation: 31952

You can create a global object as a const QString nullStr() and use it everywhere- Somewhat similar to Null Object Pattern.

Alternatively as billz mentions, a const reference to a temporary can exist, so making it const Qstring& will enable the first 2 versions

Regardless, you should change the reference to const Qstring& if you dont intend to modify it.

Upvotes: 5

billz
billz

Reputation: 45410

To bind a reference to a temporary object, you need const qualifier, if QString constructor takes char* input, try:

void SetFoo(const QString& foo);

It makes sense to pass a reference to outlived variable to SetFoo only:

void SetFoo(QString& foo);
QString s;
SetFoo(s);

. NOTE: Everything seem to work in windows environment with using vc++ compiler but I encounter the above mentioned compilation error in linux environment using g++.

VisualStudio is famous(good or bad way) for its C++ extentions, your code compiles on VS doesn't mean it's the C++ standards. The better way is to turn on compile warning(level 4) when you write code, it should give you a warning for binding a reference to temporary object.
Also lookup C++ standard, lookup compiler manuals to make sure your code is portable.

Upvotes: 2

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