C++笔记4：类型转换

一：类型转换的两种方式 1：显式类型转换：强转 c风格：(目标类型)原类型变量

int a;
float b = (float)a; 

c+风格：目标类型(原类型变量)

int a;
float b = (float)a;
int c;
float d = float(c);
int e;
float f = (float)(e);

2：隐式类型转换：编译器转

int a;
double b;
float c;
short d;
char e;

①：任何基本类型变量之间都可以隐式转换

a=b=c=d=e;
e=d=c=b=a;

②：任何类型的指针和void*都可以隐式转换

void *p = &a;
p = &b;
p = &c;
p = &d;
p = &e;

③：void*和任何其他类型指针必须强转

int *pa = (int*)(p);
double *pb = (double*)(p);
float *pc = (float*)(p);
short *pd = (short*)(p);
char *pe = (char*)(p);

④：任何类型的非常指针和同类型的常指针都可以隐式转换

const int *cpa = pa;
const double *cpb = pb;
const float *cpc = pc;
const short *cpd = pd;
const char *cpe = pe;

⑤：任何类型的常指针和同类型的非常指针必须强转

pa = (int*)(cpa);
pb = (double*)(cpb);
pc = (float*)(cpc);
pd = (short*)(cpd);
pe = (char*)(cpe);

⑥：除void*外，任何其他类型指针之间必须强转

pa = (int*)(pb);

二：类型转换 ①：静态类型转换

static_cast<目标类型>(源类型变量)

概念：隐式类型转换的逆转换和自定义类型转换

int *pa = static_cast<int*>(p);
double *pb = static_cast<double*>(p);
float *pa = static_cast<float*>(p);
short *pa = static_cast<short*>(p);
char *pa = static_cast<char*>(p);
//特殊性：虽然任何类型的非常指针可以向常指针隐式转换，但唯一特殊不可static_cast逆转换
int *pa = static_cast<int*>(cpa);
double *pb = static_cast<double*>(cpb);
float *pa = static_cast<float*>(cpc);
short *pa = static_cast<short*>(cpd);
char *pa = static_cast<char*>(cpe);

②：常类型转换(去常转换)

const_cast<目标类型>(源类型变量)

概念：去除指针或者引用上的const常属性

int *pa = const_cast<int*>(cpa);
double *pb = const_cast<double*>(cpb);
float *pa = const_cast<float*>(cpc);
short *pa = const_cast<short*>(cpd);
char *pa = const_cast<char*>(cpe);

③：重解释类型转换

reinterpret_cast<目标类型>(源类型变量)

概念：任意类型指针或引用之间转换(除void*)；任意类型指针或整形之间的转换。

pa = reinterpret_cast<int*>(pb);
pa = reinterpret_cast<int*>(100);

④：动态类型转换

dynamic_cast<目标类型>(源类型变量)

概念：多态，父子类指针或引用之间的转换。