Can someone help what is incorrect in this program? [duplicate]

Answer 1

void func(int&* ptr)
{
    ptr =  new int;
}

int main() 
{
    int* ptr;
    func(ptr);
    *ptr = 2;
}

pass pointer by reference, not by value

Answer 2

ptr is passed to funcn by value so the parameter ptr only gets the copy of ptr in main. Any changes to func's ptr would not modify main's ptr and hence memory is not allocated for the pointer ptr in main. The assignment to uninitialized pointer

*ptr = 2;    

invokes undefined behavior.

Possible solutions:

Using pointer to pointer:

void func(int** ptr)
{
    *ptr =  new int;
}

int main() 
{
    int* ptr;
    func(&ptr);
    *ptr = 2;
}  

Returning pointer from function:

int* func(int* ptr)
{
    ptr =  new int;
}

int main() 
{
    int* ptr;
    ptr = func(ptr);
    *ptr = 2;
}  

Using reference:

void func(int&* ptr)
{
    ptr =  new int;
}

int main() 
{
    int* ptr;
    func(ptr);
    *ptr = 2;
}