Why is 'volatile' parasitic in C++?
- by Steve
Consider the following code:
int main()
{
int i;
volatile int* p = &i;
int *v = p;
return 0;
}
This gives an error in g++:
$ g++ -o volatile volatile.cpp
volatile.cpp: In function ‘int main()’:
volatile.cpp:6: error: invalid conversion from ‘volatile int*’ to ‘int*’
My intention was that I want to make p volatile. However, once I've read the value of p, I don't care if accessing v is volatile. Why is it required that v be declared volatile?
This is hypothetical code of course. In a real situation you could imagine that p points to a memory location, but is modified externally and I want v to point to the location that p pointed to at the time of v = p, even if later p is externally modified. Therefore p is volatile, but v is not.
By the way I am interested in the behaviour both when this is considered C and C++, but in C this only generates a warning, not an error.
