why using std::sqrt failed if I redefine the sqrt function?

Question

#include<iostream>

double sqrt(double);

int main()
{
    double a = std::sqrt(4.0);
    std::cout << a; 
    return 0;
}

double sqrt(double a)
{
    return 1.0;
}

I know I declare the sqrt at first, but I use std::sqrt, it still call my own sqrt. why?

Cannot reproduce. Is this your *actual* code? What compiler/platform? — Adrian Mole, Jun 28 '20 at 21:41
Using Visual Studio 2019 on Windows: clang-cl compiles without warning and gives an output of `2` (i.e. `std::sqrt` is called). However, the MSVC compiler doesn't like it: **error C2169: 'sqrt': intrinsic function, cannot be defined**. — Adrian Mole, Jun 28 '20 at 21:45
@AdrianMole, in my local VS 2019 using MSVC the result is also 1. — anastaciu, Jun 28 '20 at 22:01
Maybe you have intrinsic functions disabled. But anyway, it's undefined behaviour (see dupe). — Adrian Mole, Jun 28 '20 at 22:02
I use VS 2019 and platform is Windows, I do not know how to check the compiler. it is no error on my computer, but has C28251 warning, the result on my computer is 1. — xmzhang, Jun 28 '20 at 22:05

score 0 · Answer 1 · answered Jun 28 '20 at 21:45

0

Search your code for a using namespace std; somewhere. Perhaps hidden in some other set of include files.

answered Jun 28 '20 at 21:45

Michael Chourdakis

10,345
3
42
78

1

Adding `using namespace std;` to the OP's code makes no difference to clang-cl and MSVC! Same results as in my comment to the question. – Adrian Mole Jun 28 '20 at 21:46
OP's code is **undefined behaviour** (see suggested duplicate). – Adrian Mole Jun 28 '20 at 21:56

why using std::sqrt failed if I redefine the sqrt function?

1 Answers1