重载数组下标 [] 运算符很慢 [英] overloaded array subscript [] operator slow

问题描述

我用c++编写了自己的Array类并重载了数组下标[]操作符，代码:

I have written my own Array class in c++ and overloaded the array subscript [] operator, code:

inline dtype &operator[](const size_t i) { return _data[i]; }
inline dtype operator[](const size_t i) const { return _data[i];}

其中 _data 是指向包含数组的内存块的指针.分析表明，仅此重载运算符就占用了总计算时间的 10% 左右(在长时间的蒙特卡罗模拟中，我正在使用 g++ 进行最大优化进行编译).这似乎很多，知道这是为什么吗?

where _data is a pointer to the memory block containing the array. Profiling shows that this overloaded operator alone is taking about 10% of the overall computation time (on a long monte carlo simulation, and I am compiling using g++ with maximum optimization). This seems a lot, any idea why this is?

dtype是一个double，_data是一个指向double数组的指针

edited: dtype is a double, and _data is a pointer to an array of double

推荐答案

operator[] 的 const 重载实际上返回的是副本而不是 dtype常量&.如果 dtype 很大，则副本可能很昂贵.

The const overload of operator[] is actually returning a copy instead of a dtype const &. If dtype is big, the copy might be expensive.

像这样设计原型应该可以解决这个问题:

Prototyping it like that should solve that problem :

inline dtype const & operator[] (const size_t i) const { return _data[i]; }

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