Declare a method with default arguments in C++ ( array of string)

Hi Experts,

I have the following method :

void  setState (std::string reason, bool bAfter, std::list<std::string>& allStates);

Is there a way to declare it with default arguments for bool and std::list<std::string> ?

so that I can call it in some places of my code

setState("shutdown");


Thanks,
LVL 2
bachra04Asked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

jkrCommented:
You can't provide a default argument for a 'std::list<std::string>&', since there is no NULL value for references. But why not just providing a 2nd overload for 'setState()' that only takes one argument, e.g.

void  setState (std::string reason, bool bAfter, std::list<std::string>& allStates);

// ...

void  setState (std::string reason) {

  std::list<std::string> empty_list;

  setState(reasob, true, empty_list); // call original 'setState()' with an empty list
}

Open in new window

0
phoffric\Commented:
Maybe you can handle a "null" list by checking for an empty list:
std::list<std::string> defaultStates;

void  setState (std::string reason, bool bAfter = false, std::list<std::string>& allStates = defaultStates) {
   std::cout << reason << " bAfter = " << bAfter;
   if( !allStates.empty() )
   {
      std::cout << "  " << allStates.back();
      std::cout << "  " << allStates.front();
   }
   std::cout << std::endl;
}

int main() {
   defaultStates.push_back ("ON");
   defaultStates.push_back ("OFF");
   setState("default");
   defaultStates.push_front("the end");
   setState("actual ", true, defaultStates);
}

Open in new window

0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
jkrCommented:
BTW, as a side note - you might want to consider passing the 'reason' parameter as a 'string&', too. That will avoid copying the string at each call. And also consider making it 'const'. E.g.

void  setState (const std::string reason, bool bAfter, std::list<std::string>& allStates);

// ...

void  setState (const std::string& reason) {

  std::list<std::string> empty_list;

  setState(reasob, true, empty_list); // call original 'setState()' with an empty list
}
                                          

Open in new window

0
Why Diversity in Tech Matters

Kesha Williams, certified professional and software developer, explores the imbalance of diversity in the world of technology -- especially when it comes to hiring women. She showcases ways she's making a difference through the Colors of STEM program.

jkrCommented:
>>Maybe you can handle a "null" list by checking for an empty list:

Which means that you still have t pass an empty list that has to be declared and instantiated. Does not make that very elegant to handle...
0
phoffric\Commented:
I expect that the author has a reason for wanting to pass in a default list. Personally, I rarely use defaults because once you start, it never ends, and then I think, for others, reading the code becomes a little harder in tracking down whether an overload was called or whether a function with default values was called.
0
Subrat (C++ windows/Linux)Software EngineerCommented:
In my opinion, just to achieve the default argument feature, we are creating a global list object or might be a data member. Which is totally unnecessary.
Better approach would be the calling 3-arg version from overloaded 1-arg version as told by JKR-(ID: 40459561).
0
phoffric\Commented:
I would expect that the author already has some object that represents what is desired to be the default value for the preponderance of cases. We are creating a global list object just to show how to address the author's question.
0
sarabandeCommented:
the following compiles without problems:

void  setState (std::string reason, bool bAfter = false, std::list<std::string>& allStates = std::list<std::string>())
{
    if (std::find(allStates.begin(), allStates.end(), reason) != allStates.end())
    {
        allStates.push_back(reason);
    }
}

Open in new window

so if you want a "default" which does nothing you can do it without defining a global list.

of course a "global" states list as suggested by phoffric makes more sense. you probably would provide the list by using a static get function like that:

class Global  // or use any other class ...
{
     static std::list<std::string> & getAllStates()
     {
           static std::list<std::string> allStates;
           return allStates;
     }
     ...
};

Open in new window

you could use it like:

void setState (std::string reason, bool bAfter = false, std::list<std::string>& allStates = std::list<std::string>())
{
    if (allStates.empty() == true)
    {
          allStates = Global::getAllStates();
    }
    if (std::find(allStates.begin(), allStates.end(), reason) != allStates.end())
    {
        allStates.push_back(reason);
    }
}

Open in new window


Sara
0
bachra04Author Commented:
Thanks Sara;

It is also a nice suggestion.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
C++

From novice to tech pro — start learning today.