A cast that is breaking strict-aliasing rules

Question

I have a function that takes a unsigned long* and needs to pass it to a external library that takes a unsigned int* and on this platform unsigned int/long are the same size.

void UpdateVar(unsigned long* var) {
   // this function will change the value at the address of var
   ExternalLibAtomicUpdateVar((unsigned int*)var); // lib atomically updates variable
}

This generate a warning saying that its breaking strict-aliasing rules. Are there any work arounds?

Thank you

Edit: I apologize for not being clear. The code is an atomic update so going around the library to store it is not an option. I could drop down to assembly but I'd like to do this in C++.

Answer 1

This should work:

void UpdateVar(unsigned long* var) {
   // this function will change the value at the address of var
   ExternalLibUpdateVar(reinterpret_cast<unsigned int*>(var));
}

Answer 2

void UpdateVar(unsigned long* var) {
   unsigned int x = static_cast<unsigned int>(*var);
   ExternalLibUpdateVar(&x);
   *var = static_cast<unsigned long>(x);
}