Which operator is used to access the value stored at a memory address pointed to by a pointer in C?

Question

BlackTom AI · Accepted Answer

The dereference operator (*) is used to obtain the value stored at the memory address held by a pointer.

1. Relevant knowledge points and concepts
- Pointer: a variable that stores a memory address (e.g., int *p).
- Address-of operator (&): yields the address of a variable (e.g., &x).
- Dereference operator (*): accesses the object at the address a pointer holds.
- Assignment operator (=): assigns a value to a variable.
- Arrow operator (->): accesses a member of a struct through a pointer (equivalent to (*p).member).

2. Step-by-step reasoning
- Suppose we have: int x = 10; int *p = &x;
  Step 1: &x computes the address of x (for example 0x7ff…).
  Step 2: p is assigned that address, so p stores 0x7ff….
  Step 3: *p applies the dereference operator to the address in p and yields the integer object stored there (the value 10).
- Reading value: int val = *p; // val becomes 10
- Writing through pointer: *p = 20; // stores 20 at the memory location of x, so x becomes 20

3. Intermediate calculation/example steps
- x = 10
- p = &x → p = 0x7ff…
- *p → value at 0x7ff… = 10
- *p = 20 → write 20 to 0x7ff…, now x = 20

4. Why the correct answer is correct
The dereference operator (*) is defined in C to take a pointer operand and yield the lvalue (or rvalue) stored at that memory address. It directly accesses the object pointed to by the pointer, which is exactly the operation asked for.

5. Why other options are incorrect
- Assignment operator (=): used to assign values to variables, not to access the value at an address.
- Pointer operator (->): used to access a member of a struct through a pointer (p->m is shorthand for (*p).m), not to obtain the entire value pointed to.
- Address of operator (&): returns the address of an object, the opposite of dereference.

6. Conclusion
The correct choice is Dereference operator (*), which matches the provided answer.

Which operator is used to access the value stored at a memory address pointed to by a pointer in C?单项选择题

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