Rules and exceptions for pointer comparisons?

In C/C++, the pointer comparison rules are as follows: pointers pointing to the same object are equal. Pointers to different objects are not equal. Exception: Pointers to null addresses are equal.

Rules and Exceptions for Pointer Comparison

In C/C++ programming, a pointer is a type that can store the address of other variables. Special variables. Understanding the rules of pointer comparison is crucial to mastering the use of pointers.

Rule:

• Two pointers pointing to the same object compare true (equal).
• Comparison of two pointers pointing to different objects is false (not equal).

Exception:

• The comparison is true when both pointers point to empty or null addresses.

Practical case:

The following C program demonstrates the rules and exceptions of pointer comparison:

#include <stdio.h>

int main() {
  int a = 10;
  int b = 20;
  int *ptr1 = &a;  // ptr1 指向 a
  int *ptr2 = &b;  // ptr2 指向 b
  int *nullPtr = NULL;  // 空指针

  // ptr1 和 ptr2 指向不同的对象
  if (ptr1 == ptr2) {
    printf("ptr1 和 ptr2 指向同一对象。\n");
  } else {
    printf("ptr1 和 ptr2 指向不同的对象。\n");
  }

  // ptr1 和 nullPtr 指向不同的对象
  if (ptr1 == nullPtr) {
    printf("ptr1 和 nullPtr 指向同一对象。\n");
  } else {
    printf("ptr1 和 nullPtr 指向不同的对象。\n");
  }

  // nullPtr 和 nullPtr 指向相同的空对象
  if (nullPtr == nullPtr) {
    printf("nullPtr 和 nullPtr 指向同一对象。\n");
  } else {
    printf("nullPtr 和 nullPtr 指向不同的对象。\n");
  }

  return 0;
}

Output:

ptr1 和 ptr2 指向不同的对象。
ptr1 和 nullPtr 指向不同的对象。
nullPtr 和 nullPtr 指向同一对象。

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