Default values for STL container function arguments?

Expand Post »

Quick question:

Normally when I have a function, I can make one or more of the 'last' arguments as defaults, for example:

C++ Syntax (Toggle Plain Text)
string whatever( int a, string b="NONE" )
{
//blah, blah, blah
string temp= "WHATEVER";
return temp;
}
string whatever( int a, string b="NONE" )
{
//blah, blah, blah
string temp= "WHATEVER";
return temp;
}

The benefit is that I can have one function and I can do logic in there based on whether my parameter has the default or has something else.

I would like to do the same thing, but with a parameter that is a container. How do I do it?

C++ Syntax (Toggle Plain Text)
string whateverTwo( int a, vector<string> defaultV = ????)
{
 
//whatever
string temp= "WHATEVER";
return temp;
}
string whateverTwo( int a, vector<string> defaultV = ????)
{
 
//whatever
string temp= "WHATEVER";
return temp;
}

I want this so that I can either pass in the vector or not. I know that I of course can make 2 different functions, but wanted to see if I could do a default instead. Any thoughts?

Similar Threads

Send data on a serial port in C++
help with classes?! in C++
Function Arguments in Java
Help splitting up code into .h and .cpp in C++
This Should be Easy for You Guys! in Linux Servers and Apache

winbatch

Reputation Points: 68

Solved Threads: 18

Posting Pro in Training

Offline

466 posts
since Feb 2005

Permalink

Nov 7th, 2005

Re: Default values for STL container function arguments?

Why not use a constant pointer to the vector? If the vector is not zero, then make a copy of it inside the function.

C++ Syntax (Toggle Plain Text)
string whateverTwo( int a, const vector<string> *defaultV = 0) {
    vector<string> stringVector;
    if (defaultV != 0)
        stringVector = *defaultV;
    // ...
}
string whateverTwo( int a, const vector<string> *defaultV = 0) {
    vector<string> stringVector;
    if (defaultV != 0)
        stringVector = *defaultV;
    // ...
}

Daishi

Reputation Points: 10

Solved Threads: 2

Junior Poster in Training

Offline

80 posts
since Aug 2005

Permalink

Nov 7th, 2005

Re: Default values for STL container function arguments?

STL vector objects have their own default capacity, which is implementation dependent. You should be able to determine this value rather simply. Something like this should do.

vector<int> v;
cout << "default capacity of vectors in my STL implementation is " << v.capacity <<

Of course you can specify a capacity, if you desire.

vector<int> v(5);
cout << "the capacity of v is " << v.capacity();
cout << "the size of v is ";
if(v.empty())
cout << "zero" << endl;
else
cout << v.size();

You can also specify default values.

vector<int> v(5,0);
for(int i = 0; i < 5; ++i)
cout << "v[" << i << "] = " << v[i] << ' ' ;

Data structures can be very big, meaning passing them back and forth by value can be costly. It's often wiser to pass them by reference, making them const references if you don't want the function to change any of the values in the structure being passed. So I'd declare the structure using my own defualt capacity and default all values to the desired default value and then pass that structure to a function by reference in it's current state.

Lerner

Reputation Points: 718

Solved Threads: 373

Nearly a Posting Maven

Offline

2,253 posts
since Jul 2005

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: Reading/Writing to Executable

Next Thread in C++ Forum Timeline: compile error

DaniWeb Message

Cancel Changes

User Name
Password