例1，将 double 类型转换为 int 类型
double d = 5.5;
int i = static_cast<int>(d);
printf("i = %d\n", i);
运行结果如下：
i = 5
例2，将 int 类型转换为 double 类型
int a = 10;
int b = 3;
double c = a / b;
double d = static_cast<double>(a) / static_cast<double>(b);
printf("c = %lf\n", c);
printf("d = %lf\n", d);
运行结果如下：
c = 3.000000
d = 3.333333
例3，将派生类指针转换为基类指针，由于这里是智能指针，所以 static_cast 变成了 static_pointer_cast。
// 基类
// 指向基类的智能指针
struct Sensor {};
typedef std::shared_ptr<Sensor> SensorPtr;
// 派生类
// 指向派生类的智能指针
struct CarVelocity : public Sensor {};
typedef std::shared_ptr<CarVelocity> CarVelocityPtr;
// 将派生类指针转换为基类指针
std::vector<SensorPtr> ret;
CarVelocityPtr can_measurement = std::make_shared<CarVelocity>();
ret.push_back(std::static_pointer_cast<Sensor>(can_measurement));
例4，将基类指针转换为派生类指针
std::vector<SensorPtr> measurements;
std::vector<CarVelocityPtr> vec_can_meas;
auto can_meas = std::static_pointer_cast<CarVelocity>(measurements[i]);
vec_can_meas.push_back(can_meas);
例5，将 type 类型的指针转换为空指针，将空指针转换为 type 类型的指针
type* pt_type = new type();
void* pt_void;
pt_void = static_cast<void*>(pt_type);type* pt = static_cast<type*>(pt_void);
