C++：自定义函数数据类型转换

主要代码如下：

//获取字符串的长度函数（每个汉字2个字节长度）
int GetStringLength(string str)
{
	int ret = 0;
	int i = 0;

	while (auto sss = str[i++] != '\0')
	{
		ret++;
	}
	return ret;
}

//double转化为字符串函数
string DoubleToString(double d)
{
	bool isNegative = d < 0 ? true : false;
	double high, low;

	if (isNegative)
	{
		high = std::ceil(d);
		low = high - d;
	}
	else
	{
		high = std::floor(d);
		low = d - high;
	}

	std::deque<int> intDeq, decDeq;
	int h = (int)high;

	if (isNegative)
	{
		h *= -1;		//确保是非负数//
	}
	if (h < 10)
	{
		intDeq.emplace_front(h);
	}
	else
	{
		while (h > 0)
		{
			intDeq.emplace_front(h % 10);
			h = std::floor(h / 10);
		}
	}
	if (low > 0)
	{
		int tmp = 15;		//确保小数点后15位//
		while (low > 0 && tmp-- > 0)
		{
			decDeq.emplace_back(std::floor(10 * low));
			low = 10 * low;
			low -= std::floor(low);
		}
	}
	else
	{
		decDeq.emplace_back(0);
	}

	std::string retVal;
	retVal.resize(intDeq.size() + decDeq.size() + 2);
	int i = 0;
	for (const auto& e : intDeq)
	{
		retVal[i++] = e + 48;
	}
	retVal[i++] = '.';
	for (const auto& e : decDeq)
	{
		retVal[i++] = e + 48;
	}

	if (isNegative)
	{
		retVal = "-" + retVal;
	}

	return retVal;
}

//字符串转换为double函数
double StringToDouble(string str)
{
	std::deque<int> intDeq, decDeq;
	bool isFindDot = false;
	int i = 0;

	while (str[i] != '\0')
	{
		if (str[i] == '.')
		{
			isFindDot = true;
		}
		if (str[i] >= '0'&&str[i] <= '9')
		{
			auto ch = str[i] - 48;
			if (isFindDot)
			{
				decDeq.emplace_back(ch);
			}
			else
			{
				intDeq.emplace_front(ch);
			}
		}
		i++;
	}

	double retVal = 0.0;
	i = 0;
	for (const auto& e : intDeq)
	{
		retVal += e * std::pow(10.0, 1.0 * i++);
	}
	i = 1;
	for (const auto& e : decDeq)
	{
		retVal += e * std::pow(10.0, (-1.0) * i++);
	}
	return retVal;
}
           

测试代码如下：

int nLen = GetStringLength("a345阖家欢乐fF;$%^");
	auto ff1 = StringToDouble(".12");
	auto ff2 = StringToDouble("12.345");
	auto ff3 = StringToDouble("123.45g.67Y");

	auto ss1 = DoubleToString(12.345);
	auto ss2 = DoubleToString(-16.10001);

	cout << nLen << '\t' << ff1 << '\t' << ff2 << '\t' 
		<< ff3 << '\t' << ss1 << '\t' << ss2 << endl;
           

运行结果如下：

18      0.12    12.345  123.457 12.345000000000000