Assigning Value to Array in Constructor

Question

I'm working at creating a class that is a binary tree. I would like to simplify this by creating a class that stores the data in an array, and then go back and make the magic happen.

However, the commented out line in the following section of code causes Visual Studio to spew ton of errors. It makes sense to me, but for some reason it won't compile. I'm not a C++ guy, but after a lot of Googling, nothing is working for me.


template 
class bin_tree
{
private:
    int *data;

public:
    int getData(int x)
    {
        return 1;
    };
    bin_tree() : data(new int[4])
    {
        //data = {1, 2, 3, 4};
    };
};

Why did you put the word template at the beginning of your class definition? — jogojapan
– jogojapan, Commented Nov 10, 2012 at 0:53
@psyklopz: So you're just writing random keywords hoping a program comes out at the end? That is not the way to go. Read a C++ book and get yourself back up to speed. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Nov 10, 2012 at 1:14
Thanks, but I have no desire to learn C++. I have a small problem and a large deadline. — psyklopz
– psyklopz, Commented Nov 10, 2012 at 1:26

Evgeny Panasyuk · Accepted Answer · 2015-04-15 23:22:26Z

1

If size of your array is fixed (from your code, seems like it is the case), then you don't need to do dynamic allocation (i.e. "new").

http://coliru.stacked-crooked.com/a/97e112739e8a45de

class bin_tree
{
private:
    int data[4];

public:
    int getData(int)
    {
        return 1;
    };
    bin_tree()
        : data{1, 2, 3, 4} // C++11
    {
        // or:
        data[0] = 11;
        data[1] = 22;
        // ...
    };
};

#include <iostream>
int main()
{
    bin_tree tr;
    std::cout << "OK";
}

edited Apr 15, 2015 at 23:22

answered Nov 10, 2012 at 0:55

Evgeny Panasyuk

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4 Comments

Nik Bougalis Over a year ago

the bin_tree() : data{1, 2, 3, 4} { ... } syntax is valid only in a C++11 compliant compiler.

Evgeny Panasyuk Over a year ago

@NikB. I know this. Current C++ is C++11, read "Zoidberg'--" comment at stackoverflow.com/a/13223531/1762344

Nik Bougalis Over a year ago

You may, but psyklopz (who mentions not having used C++ for 5 years) may not. It's fine and dandy to show the C++11 syntax, but you should at least explain it (or make a note in the code you show). At least that's my take on it.

Evgeny Panasyuk Over a year ago

In fact, I have added "C++11" in-code comment, before read your comment

justin · Accepted Answer · 2012-11-10 01:19:46Z

1

Welcome to C++. Use std::array for a fixed size array:

#include <array>

class bin_tree {
private:
    std::array<int, 4>data;
public:    
    bin_tree() : data({1, 2, 3, 4}) {
    }
    ...
};

If you need dynamic resizing, then use std::vector instead.

edited Nov 10, 2012 at 1:19

answered Nov 10, 2012 at 1:03

justin

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9 Comments

Evgeny Panasyuk Over a year ago

What the point of using std::array in that particular example (instead of old-style array) ?

justin Over a year ago

@EvgenyPanasyuk because i am encouraging it as the default go-to fixed size array representation. esp. for somebody who's "not a C++ guy". it provides a clear interface, error detection, good semantics. it's also effectively weightless in many regards. i think the inverse question should be asked -- why use new[] or a c array (as in your answer) in this case? the OP's implementation is likely more complex than the implementation required to demonstrate the problem.

Evgeny Panasyuk Over a year ago

"clear interface" - bloated with named member functions (though understandable reasons). "error detection" - yes, I think this is definitely advantage even for that particular case, I forgot about this opportunity. "good semantics" - what do you mean exactly(value-semantic with copy?) ?

justin Over a year ago

@EvgenyPanasyuk alright… so you don't like std::array. i'm not following your lead to where you want to take the discussion. chau.

Benjamin Lindley Over a year ago

@EvgenyPanasyuk: Why wouldn't you use it? It's not bloated, as you suggest. Those member functions cost nothing, where nothing = an insignificant micro-fraction of a second of compile time. The question really should be, is there any particular reason you should use an old-style array here? Does it offer anything (significant) that std::array does not?

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