Why same function with or without const ?

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i found the code below for OpenCV 2.4.13

------------------------core.hpp---------------------------------
1920: uchar* ptr(int i0=0);
const uchar* ptr(int i0=0) const;

template<int n> uchar* ptr(const Vec<int, n>& idx);
template<int n> const uchar* ptr(const Vec<int, n>& idx) const;
------------------------------------------------------------------
there are two declaration for same function and template uchar* ptr(), with and without const;
how compiler will handle this? why need write these two version?

What I have tried:

how compiler will handle this? why need write these two version?

Posted 13-Dec-17 3:55am

wing_wang08

Updated 13-Dec-17 4:55am

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Jochen Arndt · Answer 1 · 2017-12-13T04:55:00

The compiler chooses the version that matches in the context:

C++

// The const version is used here
uchar c = *var.ptr();
const uchar *p = var.ptr();

// The non const version is used here
*var.ptr() = c;
uchar *p = var.ptr();

It is not really necessary to provide the const version but it is recommended, good style, and prevents from changing values inadvertently where this is checked at compile time:

C++

// The const version is used here
const uchar *p = var.ptr();
// Will throw a compiler error
*p = c;