我有一个简单的二维线类,其中包含两个 double vector 。我添加了getValue和setValue函数,但是希望公共(public)接口(interface)在这些函数旁边提供方括号运算符。以下代码显示了实现和使用:
#include <vector>
#include <algorithm>
#include <cassert>
class Simple2DLine
{
public:
Simple2DLine();
// Simple read method with linear interpolation
double getValue(double x) const;
// Simple write method, adds a curve point, keeping the arrays sorted
void setValue(double x, double y);
double& operator [](double x);
const double operator [](double x) const;
private:
std::vector<double> m_X;
std::vector<double> m_Y;
int getNearestIndex(double x) const;
};
Simple2DLine::Simple2DLine()
{
}
void Simple2DLine::setValue(double x, double y)
{
// Get the index of the point at or just before 'x'
int idx = getNearestIndex(x);
// Check if the exact point already exists.
if (idx >= 0)
{
if (m_X[idx] == x)
{
m_Y[idx] = y;
return;
}
else
{
// Insert adds the value just BEFORE idx, so increment it before inserting.
++idx;
m_X.insert(m_X.begin() + idx,x);
m_Y.insert(m_Y.begin() + idx,y);
return;
}
}
// Otherwise, just insert at the front.
m_X.insert(m_X.begin(),x);
m_Y.insert(m_Y.begin(),y);
}
double Simple2DLine::getValue(double x) const
{
// Make sure there are points - if not, return 0.
if (m_X.size() == 0)
{
return 0;
}
// Make sure it's not out of bounds.
if (x < m_X.front() || x > m_X.back())
{
return 0;
}
// Check if it's at or after the last point
if (x == m_X.back())
{
return m_X.back();
}
// Find the point just before the given point.
int idx = getNearestIndex(x);
// Check if we're on the exact point
if (m_X[idx] == x)
{
return m_X[idx];
}
else
{
// Find the distance from the nearest point and linearly interpolate.
double dist = x - m_X[idx];
return m_Y[idx] + dist * (m_Y[idx + 1] - m_Y[idx]) / (m_X[idx + 1] - m_X[idx]);
}
}
double& Simple2DLine::operator [](double x)
{
// Create a space for the new value
setValue(x,0.0);
int idx = getNearestIndex(x);
return m_Y[idx];
}
const double Simple2DLine::operator [](double x) const
{
return getValue(x);
}
// Returns the index of the point at or just before 'x'. Invalid values return -1.
int Simple2DLine::getNearestIndex(double x) const
{
if (m_X.empty())
{
return -1;
}
std::vector<double>::const_iterator xBegin(m_X.begin());
std::vector<double>::const_iterator xEnd(m_X.end());
// Get an iterator to the first value GREATER than our search value
std::vector<double>::const_iterator it = upper_bound(xBegin,xEnd,x);
// If the iterator is at the beginning, all values are greater
if (it == xBegin)
{
return -1;
}
// Otherwise, decrement the iterator by 1, and return its' distance from the start.
return (it - 1) - xBegin;
}
int main(int argc, char** argv)
{
Simple2DLine tda;
tda.setValue(0.0,10.0);
tda.setValue(1.0,15.0);
tda.setValue(2.0,20.0);
tda.setValue(3.0,25.0);
double tmp = tda.getValue(0.5);
assert(abs(tmp - 12.5) < 0.000001);
tmp = tda.getValue(1.5);
assert(abs(tmp - 17.5) < 0.000001);
tmp = tda.getValue(2.5);
assert(abs(tmp - 22.5) < 0.000001);
// Here, the wrong version of the overridden operator is being called.
tmp = tda[1.5];
tda[2.5] = 22.5;
}
当我以以下方式访问行对象时,将调用正确版本的运算符(非const)
tda[2.5] = 22.5;
但是,当我尝试使用const版本时,如下所示:
tmp = tda[1.5];
非常量版本被调用。我的实现中有错误吗?还是无法以这种方式访问类(class)?
最佳答案
在const对象上调用const版本。因此,如果您有一个声明为const Simple2DLine tda
的对象,则将调用operator[]
的const重载版本。
实际上,您将const
对象视为函数参数,例如:
void foo(const Simple2DLine& tda)
{
std::cout<< tda[0];
}
在那里,您会注意到const重载函数被调用。
同样,您的
const
重载operator[]
仍然可以返回引用。关于c++ - 在类中调用的错误版本的覆盖[]运算符,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/20215972/