C语言常量指针

示例

单指针

• 指向一个指针 int

  指针可以指向不同的整数，并且int可以通过指针更改。此代码示例将b指向，int b然后将其b值更改为100。

  int b;
  int* p;
  p = &b;    /* OK */
  *p = 100;  /* OK */
  

• 指向一个指针 const int

  指针可以指向不同的整数，但int不能通过指针更改的值。

  int b;
  const int* p;
  p = &b;    /* OK */
  *p = 100;  /* Compiler Error */
  

• const 指向 int

  指针只能指向1，int但int可以通过指针更改其值。

  int a, b;
  int* const p = &b; /* OK as initialisation, no assignment */
  *p = 100;  /* OK */
  p = &a;    /* Compiler Error */
  

• const 指向 const int

  指针只能指向一个，int并且int不能通过指针更改。

  int a, b;
  const int* const p = &b; /* OK as initialisation, no assignment */
  p = &a;   /* Compiler Error */
  *p = 100; /* Compiler Error */
  

指针到指针

• 指向一个指针的指针 int

  这段代码将的地址分配p1给double指针p（然后指向）int* p1（指向int）。

  然后更改p1为指向int a。然后将a的值更改为100。

  void f1(void)
  {
    int a, b;
    int *p1;
    int **p;
    p1 = &b; /* OK */
    p = &p1; /* OK */
    *p = &a; /* OK */
    **p = 100; /* OK */
  }
  

• 指向a的指针 const int

   void f2(void)
  {
    int b;
    const int *p1;
    const int **p;
    p = &p1; /* OK */
    *p = &b; /* OK */
    **p = 100; /* error: assignment of read-only location ‘**p’ */
  }
  

• 指向const一个指针的指针int

  void f3(void)
  {
    int b;
    int *p1;
    int * const *p;
    p = &p1; /* OK */
    *p = &b; /* error: assignment of read-only location ‘*p’ */
    **p = 100; /* OK */
  }
  

• const 指向的指针 int

  void f4(void)
  {
    int b;
    int *p1;
    int ** const p = &p1; /* OK as initialisation, not assignment */
    p = &p1; /* error: assignment of read-only variable ‘p’ */
    *p = &b; /* OK */
    **p = 100; /* OK */
  }
  

• 指向的const指针const int

  void f5(void)
  {
    int b;
    const int *p1;
    const int * const *p;
    p = &p1; /* OK */
    *p = &b; /* error: assignment of read-only location ‘*p’ */
    **p = 100; /* error: assignment of read-only location ‘**p’ */
  }
  

• const 指向的指针 const int

  void f6(void)
  {
    int b;
    const int *p1;
    const int ** const p = &p1; /* OK as initialisation, not assignment */
    p = &p1; /* error: assignment of read-only variable ‘p’ */
    *p = &b; /* OK */
    **p = 100; /* error: assignment of read-only location ‘**p’ */
  }
  

• const指向的const指针int

  void f7(void)
  {
    int b;
    int *p1;
    int * const * const p = &p1; /* OK as initialisation, not assignment */
    p = &p1; /* error: assignment of read-only variable ‘p’  */
    *p = &b; /* error: assignment of read-only location ‘*p’ */
    **p = 100; /* OK */
  }