const指针与指向const的指针
const指针
- 如下代码：
int main() {
int num = 42;
int* const p = # // p是常量指针，指向一个整型数
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
num = 76; // 修改p所指向的内存的值
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
运行结果：
可以看出，num被成功修改，*p发生了改变，即p指向的那段内存空间的值可以改变，const在这里修饰指针p。
- 如下代码：
int main() {
int num = 42;
int* const p = # // p是常量指针，指向一个整型数
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
int num2 = 76;
p = &num2; // 此处编译时报错，试图修改p的指向
cout << "num = " << num << endl;
cout << "num2 = " << num2 << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
编译报错：
报错指出，p的指向无法修改，因为const在这里修饰的是指针本身p。
指向const的指针
- 如下代码：
int main() {
const int num = 10086;
const int* p = # // p是指向常量的指针
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
*p = 10088; // 编译报错，试图修改*p
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
编译报错：
num声明为const，显然不能直接修改，当通过使用指向num的指针p来修改时，也行不通。
- 如下代码：
int main() {
const int num = 10086;
const int* p = # // p是指向常量的指针
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
const int num2 = 10010;
p = &num2; // 修改p的指向
cout << "num = " << num << endl;
cout << "num2 = " << num2 << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
运行结果：
可以看出，p的指向发生了改变，显然这里的const修饰的是p所指向的内容。
- 注意如下代码：
int main() {
const int num = 10086;
int* p = # // 编译报错
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
编译报错：
const内容无法赋值给普通的指针，只能赋给用const修饰类型的指针。
指向const的const指针
- 如下代码：
int main() {
const int num = 100;
const int* const p = #
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
*p = 99; // 编译报错，试图修改*p的值
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
编译报错：
- 如下代码：
int main() {
const int num = 100;
const int* const p = #
cout << "num = " << num << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
const int num2 = 99;
p = &num2; // 编译报错，试图修改p的指向
cout << "num = " << num << endl;
cout << "num2 = " << num2 << endl;
cout << "p = " << p << endl;
cout << "*p = " << *p << endl << endl;
return 0;
}
编译报错：
- 总结：
const在*之后时修饰的是指针本身，表示指针指向不可变；
const在*之前时修饰的是指针所指向的内容，表示这部分值不可变；
