function returning pointer of its local vairable

[akshay202]

Can some body please help me understand the output of this c++ programs , its giving erratic results

#include <cstdio>
#include<iostream>
using namespace std;

float* area ( float radius );  

int main()
{
float rad = 1;
float *ar;
ar = area(rad);
cout<<(*ar);
cout<<" "<<(*ar);
cout<<endl;
cout<<(*ar);
cout<<"\n";
cout<<(*ar);
cout<<endl;
cout<<(*ar);
fflush(stdin);
cout<<" "<<(*ar);

}

float* area ( float radius )
{
float a=0;
float *areaPtr = &a;
a =  (3.14 * radius * radius);
return(areaPtr);
}

when I print the value of (*ar) it comes out different each time , the output is

3.14 1.85048e-38
2.26799e-38
0
1.85048e-38 0

[helios]

Returning pointers and references to local objects or variables has undefined behavior because the data goes out of scope when the function returns. In other words, don't do it.

[akshay202]

If behavior of returning address of local variable of a function is undefined then what is the use of a function returning pointer... like if a pointer is made global and used inside a function , or is passed to a function as one of its arguments and the function is doing manipulation at that address then it doesn't need to return that address.

[Galik]

Well you can return a pointer to data allocated from the free-store with new:

char* ptr = new char[1024];
return ptr;