Take variable number of arguments and put them in std::vector

Question

I'm making a class - let's call it Container - that is basically just containing a std::vector and some special logic that decides how are the vector values picked. I want to add a method for adding multiple values to my class with one call. This is my method that adds one item:

void LoopGenerator::add(RandomStripe &stripe)
{
    stripes.push_back(new SingleStripe(stripe));
}

I'd like a similar method that would be called like this:

LoopGenerator gen = LoopGenerator();
gen.add(RandomStripe(), RandomStripe(), RandomStripe() ... and as much as you want ... );

and would add all parameters to the inner std::vector.

Is this possible to do just with standard libraries, or best without them?

A traditional va_args would require some way to know how many parameters were passed. Alternatively, you can use variadic templates, if available. — Raymond Chen, Dec 05 '14 at 21:03
@Tomáš Zato What are RandomStripe and SingleStripe? Are they different types? — Vlad from Moscow, Dec 05 '14 at 21:07
@VladfromMoscow Yes, they are different. Actually, `SingleStripe` just exists so `RandomStripe` can be with array along with other stripe generating classes... `SingleStripe` derives from same class as `LoopGenerator`. — Tomáš Zato, Dec 05 '14 at 21:26

score 5 · Accepted Answer · answered Dec 05 '14 at 21:13

5

You can use std::initializer_list. For example

#include <initializer_list>
#include <algorithm>
#include <vector>
#include <iterator>    


//...

void LoopGenerator::add( std::initializer_list<RandomStripe> stripe )
{
    std::transform( stripe.begin(), stripe.end(), 
                   std::back_inserter( stripes ),
                   []( const RandomStripe &s ) { return new SingleStripe( s ); } );
}

And call it like

gen.add( { RandomStripe(), RandomStripe(), RandomStripe(), /*...*/ } );

answered Dec 05 '14 at 21:13

Vlad from Moscow

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I was rewriting the code so it took me a while to get to using your answer. I get following error: `cannot open source file "initializer_list"` Should I reconfigure my project? – Tomáš Zato Dec 06 '14 at 20:29
@Tomáš Zato What compiler are you using? Does it support C++ 2011? – Vlad from Moscow Dec 06 '14 at 20:32
[Quick search](http://stackoverflow.com/a/10849807/607407) suggests that it doesn't. But I'm working in MS Visual Studio. It's quite complex and confusing. Maybe it could be enabled somewhere. – Tomáš Zato Dec 06 '14 at 21:11
@Tomáš Zato What is the version of MS VS? – Vlad from Moscow Dec 06 '14 at 21:29

score 0 · Answer 2 · answered Dec 05 '14 at 21:12

0

If you have C++11 you could utilize variadic templates to accomplish this.

In prior versions I would suggest just doing method chaining:

LoopGenerator& LoopGenerator::add(RandomStripe &stripe)
{
    stripes.push_back(new SingleStripe(stripe));
    return *this;
}

And call it gen.add(RandomStripe()).add(RandomStripe()).add(RandomStripe());

answered Dec 05 '14 at 21:12

Mark B

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as the number of elements to be added to stack increases should user change the code to add one more call of function add() ? – Muhammet Ali Asan Dec 05 '14 at 21:40

Take variable number of arguments and put them in std::vector

2 Answers2