Why I am getting a garbage value in VS code and when I run this code in the online compiler it gives correct value?

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C++

#include <iostream>
using namespace std;
class Box
{
    private:
    int length;
    public:
    void show()
   { int a;
    cout<<"Hie";}
    friend int printlength (Box); //friend function
};
int printlength (Box b)
{
    b.length +=10;
    return b.length;

}
int main()
{
    Box b;
    cout<<"length of box:"<<printlength (b)<<endl;
    return 0;
}

What I have tried:

C++

#include <iostream>
using namespace std;
class Box
{
    private:
    int length;
    public:
    void show()
   { int a;
    cout<<"Hie";}
    friend int printlength (Box); //friend function
};
int printlength (Box b)
{
    b.length +=10;
    return b.length;

}
int main()
{
    Box b;
    cout<<"length of box:"<

Posted 13-Feb-22 19:52pm

Tech World Feb2022

Updated 14-Feb-22 10:13am

Sean Ewington

v2

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OriginalGriff · Answer 1 · 2022-02-13T20:13:00

Simple: you don't initialise any values.
You create an instance of a Box:

C++

Box b;

but that doesn't assign any value to length before you try to use it:

C++

Box b;
cout<<"length of box:"

Different compilers will treat this situation differently: some will zero the memory for you, others will not - so two different compilers (or even just the switches applied when it is compiled) will produce different results.

Since a box can't have no dimensions and still be a box, a default parameterless constructor is probably fairly useless and one that takes a length, depth, and height might be a better idea ...

CPallini · Answer 2 · 2022-02-13T20:21:00

Solution 2

In your code, the length data member is default-initialized to undeterminate value, hence, in order to have consistent outputs you have to explicitely initialize it.
See Default initialization - cppreference.com[^] (the code sample clarifies it).

Posted 13-Feb-22 20:21pm

CPallini

KarstenK · Answer 3 · 2022-02-13T23:44:00

The reason is because you have used two different compilers: the online tool and your local compiler. And in C/C++ is the value of uninitialized memory undeterminaterd., but the online compiler has added the feature of zeroing it out.
So it is doing some extra work which slows performance and costs energy in real life. That is fine for a lazy programmer but it hurds end users time and energy bill. ;-)

Why I am getting a garbage value in VS code and when I run this code in the online compiler it gives correct value?

3 solutions

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