我之前提出了一个问题:为什么dynamic_cast被认为是邪恶的?回答让我写了一些关于
代码如下:
结果如下:
硬件和操作系统:
dynamic_cast
性能的代码。我编译并测试了这段代码,使用dynamic_cast
会稍微比不使用dynamic_cast
花费更多的时间。我没有看到dynamic_cast
造成时间消耗的证据。我的代码正确吗?代码如下:
class Animal
{
public:
virtual ~Animal(){};
};
class Cat : public Animal
{
public:
std::string param1;
std::string param2;
std::string param3;
std::string param4;
std::string param5;
int param6;
int param7;
};
bool _process(Cat* cat)
{
cat->param1 = "abcde";
cat->param2 = "abcde";
cat->param3 = "abcde";
cat->param4 = "abcde";
cat->param5 = "abcde";
cat->param6 = 1;
cat->param7 = 2;
return true;
}
bool process(Animal *ptr)
{
Cat *cat = dynamic_cast<Cat*>(ptr);
if (cat == NULL)
{
return false;
}
_process(cat);
return true;
}
int main(int argc, char* argv[])
{
/*
argv[1] : object num
*/
if (argc != 2)
{
std::cout << "Error: invalid argc " << std::endl;
return -1;
}
int obj_num = atoi(argv[1]);
if (obj_num <= 0)
{
std::cout << "Error: object num" << std::endl;
}
int c = 0;
for (; c < obj_num; c++)
{
Cat cat;
#ifdef _USE_CAST
if (!process(&cat))
{
std::cout << "Error: failed to process " << std::endl;
return -3;
}
#else
if (!_process(&cat))
{
std::cout << "Error: failed to process " << std::endl;
return -3;
}
#endif
}
return 0;
}
使用以下方式编译:
g++ -D_USE_CAST -o dynamic_cast_test dynamic_cast_benchmark.c
g++ -o dynamic_cast_no_test dynamic_cast_benchmark.c
使用数字1、10、100等执行它们:
$time ./dynamic_cast_test num
$time ./dynamic_cast_no_test num
结果如下:
dynamic_cast non_dynamic_cast
num 10,000
real 0m0.010s real 0m0.008s
user 0m0.006s user 0m0.006s
sys 0m0.001s sys 0m0.001s
100,000
real 0m0.059s real 0m0.056s
user 0m0.054s user 0m0.054s
sys 0m0.001s sys 0m0.001s
1,000,000
real 0m0.523s real 0m0.519s
user 0m0.517s user 0m0.511s
sys 0m0.001s sys 0m0.004s
10,000,000
real 0m6.050s real 0m5.126s
user 0m5.641s user 0m4.986s
sys 0m0.036s sys 0m0.019s
100,000,000
real 0m52.962s real 0m51.178s
user 0m51.697s user 0m50.226s
sys 0m0.173s sys 0m0.092s
硬件和操作系统:
OS:Linux
CPU:Intel(R) Xeon(R) CPU E5607 @ 2.27GHz (4 cores)