Casting twice in the same line

Question

I saw this code in project.

b\'s type is void*:

void *b = ...;
int a = (int) (unsigned long) b;

Is this line

Answer 1

Directly typecasting to pointer to smaller type say int may result in compilation error on some compiler (like Clang) under x64 bit environment.

For example:

 void *p = GetSomeAddress;
 int i = (int)p;  //error on compilers like Clang.

Solution is:

int i = (int)(unsigned long)p;

or

int i = (int)(long)p;

This is because, on Unix, under LP64 model, long is 64-bit.

Such cases, you need to look thoroughly that why you need typecast from pointer to int or other smaller type which can result in loss of the data.

This question may also help you. How should I handle "cast from ‘void*’ to ‘int’ loses precision" when compiling 32-bit code on 64-bit machine?