Is it meaningful???

[vivhari]

I just tried using an STL component in sizeof() and expected an error.
But, it compiled and it had printed an answer as follows...

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.
.
#define show(x) cout<<#x<<" = "<<x<<endl
vector<int> v1(5,0);
show(sizeof(v1)/sizeof(int));//prints 3
show(v1.size());// prints 5
.
.

Can anyone tell how or why?

[weaknessforcats]

v1.size() is the number of elements in the vector. vector must be implemented as an array so there are 5 elements in the array.

sizeof reports the amount of stack memory used. What leads you to believe the array is on the stack? I mean, the vector size is changeable but a stack array is not.

Read your vector template and you will see how much of it is on the stack. Most likely there is a pointer ti the array and maybe a counter for the number of elements.

It all means your sizeof calculation is meaningless.