作为一项练习,我尝试在C++中创建一个简单的数字范围类。它将允许您遍历均匀分布的双精度浮点数(类似于numpy/Python的arange
):
我想要做的(但使用迭代器):
double lower = ..., upper = ..., delta = ...;
for (double val = lower; val < upper; val += delta)
{
// do something with val
f(val);
}
// include the last val to guarantee upper is included or exceeded
f(val); // do something with val
期望的等效迭代器代码:
double lower = ..., upper = ..., delta = ...;
NumericRange nr(lower, upper, delta);
for (NumericRange::const_iterator iter = nr.begin(); iter != nr.end(); iter++)
{
f(*iter);
}
我希望我的迭代器与STL迭代器兼容,以便可以重用代码(通过NumericRange迭代应该等同于通过std::vector迭代)。
我成功地将值存储在std::vector中(然后使用std::vector的迭代器)。这是我在线上找到的所有解决方案。然而,完全没有必要存储整个列表。
有没有一种方法可以避免存储完整的值集?有没有一些可迭代的类可以继承并覆盖++、==等来实现所需的效果,而不存储std::vector?
(我真的很想知道如何在没有BOOST的情况下做到这一点,即使BOOST很好。我之所以这样问是因为我想学习如何从头开始编写像BOOST这样的东西。我肯定知道软件工程的一部分是使用别人创建的工具,但我真的想学习这些工具的设计和构建方式。)
我的可迭代NumericRange类(内部使用std::vector):
class NumericRange
{
protected:
double lower, upper, delta;
std::vector<double> sorted_range;
public:
typedef std::vector<double>::const_iterator const_iterator;
NumericRange()
{
lower = upper = delta = std::numeric_limits<double>::quiet_NaN();
// vector is constructed empty
}
NumericRange(double lower_param, double upper_param, double delta_param)
{
lower = lower_param;
upper = upper_param;
delta = delta_param;
assert(upper_param > lower_param);
double val;
// note: can be much faster without push_back
for (val = lower_param; val < upper_param; val += delta_param)
{
sorted_range.push_back(val);
}
// ensure the upper_value is contained or surpassed
sorted_range.push_back(val);
}
// to prevent comparison of the entire vector
bool operator ==(const NumericRange & rhs) const
{
return lower == rhs.lower && upper == rhs.upper && delta == rhs.delta;
}
// note: this class doesn't really need to store the values in a
// vector, but it makes the iterator interface much easier.
const_iterator begin() const
{
return sorted_range.begin();
}
const_iterator end() const
{
return sorted_range.end();
}
double get_lower() const
{
return lower;
}
double get_upper() const
{
return upper;
}
double get_delta() const
{
return delta;
}
size_t size() const
{
return sorted_range.size();
}
void print() const
{
std::cout << "[ " << lower << " : " << upper << ": +=" << delta << " ]" << std::endl;
}
};