The C address-of operator, &, produces a pointer containing an object’s address. Passing addresses lets a function operate on objects outside its local variables, as double_swap does with two double objects. section 11.1.1
double_swap(&d0, &d1);
The call passes the addresses of d0 and d1, rather than copying their values into double_swap. section 11.1.1
void double_swap(double* p0, double* p1) {
double tmp = *p0;
*p0 = *p1;
*p1 = tmp;
}
!@%STYLE%@!
{"css":"{\"css\": \"font-weight: bold;\"}","target":"[[{\"line\":0,\"ch\":0},{\"line\":0,\"ch\":4}],[{\"line\":0,\"ch\":5},{\"line\":0,\"ch\":11}],[{\"line\":1,\"ch\":2},{\"line\":1,\"ch\":8}],[{\"line\":0,\"ch\":5},{\"line\":0,\"ch\":11}],[{\"line\":1,\"ch\":2},{\"line\":1,\"ch\":8}],[{\"line\":0,\"ch\":5},{\"line\":0,\"ch\":11}],[{\"line\":1,\"ch\":2},{\"line\":1,\"ch\":8}]]"}
!@%STYLE%@!
The pointer parameters receive those addresses; *p0 and *p1 designate the corresponding objects so the function can swap their contents. section 11.1.1
Keep these two uses of * distinct:
- In a declaration such as double*, * creates a pointer type. section 11.1.1
- In an expression such as *p0, * is the object-of operator: it dereferences the pointer and accesses its referred object. section 11.1.1
- Using * with a null or indeterminate pointer has undefined behavior. section 11.1.1
Because addresses can be passed through different parts of a program, pointers also connect the address-of operator to memory state and aliasing. Two pointers may access the same object; except for character types, only pointers with the same base type may alias. section 12.3
Practice
Write a function that receives pointers to three objects and shifts their values cyclically. section 11.1.1
