关于string的一些测试

#include 
#include 
#include  
using namespace std;
class spender
{
public:
	spender(string strfun) :strfun(strfun)
	{
		t1 = std::chrono::steady_clock::now();
	}
	~spender()
	{
		auto t2 = std::chrono::steady_clock::now();
		double dr_ms = std::chrono::duration<double, std::milli>(t2 - t1).count();
		printf("%s耗时:%.3fms\n", strfun.c_str(), dr_ms);
	}
private:
	decltype(std::chrono::steady_clock::now()) t1;
	string strfun;
};

string Remove_Space1(string str)
{
	string result;
	for (int i = 0; i < str.length(); i++)
	{
		if (!isspace(str[i]))
		{
			result = result + str[i];
		}
	}

	return result;
}

string Remove_Space2(string str)
{
	string result;
	for (int i = 0; i < str.length(); i++)
	{
		if (!isspace(str[i]))
		{
			result  += str[i];
		}
	}

	return result;
}

string Remove_Space3(string str)
{
	string result;
	result.reserve(str.length());
	for (int i = 0; i < str.length(); i++)
	{
		if (!isspace(str[i]))
		{
			result += str[i];
		}
	}

	return result;
}

string Remove_Space4(const string &str)
{
	string result;
	result.reserve(str.length());
	for (int i = 0; i < str.length(); i++)
	{
		if (!isspace(str[i]))
		{
			result += str[i];
		}
	}

	return result;
}

void main()
{

	
	string s = "hello world,hello world,hello world,hello world,hello world,\
		hello world,hello world,hello world,hello world,hello world,hello world,hello world,hello world,hello world!";

	{
		spender t("Remove_Space1");
		string strtmp = Remove_Space1(s); 
		printf("%s\n",strtmp.c_str());
	}

	{
		spender t("Remove_Space2");
		string strtmp = Remove_Space2(s);
		printf("%s\n", strtmp.c_str());
	}

	{
		spender t("Remove_Space3");
		string strtmp = Remove_Space3(s);
		printf("%s\n", strtmp.c_str());
	}

	{
		spender t("Remove_Space4");
		string strtmp = Remove_Space4(s);
		printf("%s\n", strtmp.c_str());
	}

	system("pause");
}

结果：

从运行结果可以看出第一种方式最耗时，至于它的原因：result = result + str[i];是对象的拷贝而非移动，导致反复分配，释放内存和无畏地进行字符串复制。