Trouble with function overloading

Question

I am trying to create a program where I overload a function to find the maximum between 2, 3, or 4 parameters. My code seems a bit wonky at the moment, whenever I run it I recieve the dreaded red line under "#include " and the three parameter function call. When I disable it //, the 2 and 4 parameters are fine but my 3 parameter one is no good. Would one of you mind taking a look at it and try to help? Thank you!

#include <cstdlib>
#include <iostream>

using namespace std;


double max (double, double, double, double);


int main(int argc, char** argv) {

double result;

result = max(10.0, 20.0);
cout << "Max(10.0, 20.0) = " << result << endl;
result = max(11.5, 21.2, 5.3);
cout << "Max(11.5, 21.2, 5.3) = " << result << endl;
result = max(1.8, 2.2, 1.7, 2.1);
cout << "Max(1.8, 2.2, 1.7, 2.1) = " << result << endl;
return 0;


}

double max(double a, double b)
{
if (a > b)
    return a;
else 
    return b;
}

double max(double a, double b, double c)
{
if (a > b && a > c)
    return a;

else if (b > a && b > c)
    return b;

else
    return c;
}

double max(double a, double b, double c, double d)
{
if (a > b && a > c && a > d)
    return a;
else if (b > a && b > c && b > d)
    return b;
else if (c > d)
    return c;
else 
    return d;
}

`max` is already defined in the `std` namespace. Remove `using namespace std;` from your program. — Richard Critten, Oct 30 '17 at 22:28
So for 2 variables, std::max is being used, because it is not declared, and for the 4 variable case, the overloaded function is being used. 3 variable function is not declared, so you are getting an error. — anotherone, Oct 30 '17 at 22:35

score 2 · Answer 1 · answered Oct 30 '17 at 22:28

2

Get rid of using namespace std; you are otherwise causing an ambiguity between your functions and std::max.

In general using namespace std is considered bad practice and causes problems exactly like you are seeing.

answered Oct 30 '17 at 22:28

Cory Kramer

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score 2 · Answer 2 · answered Oct 30 '17 at 22:30

You have not declared the overload with three parameters before you use it.

Add

double max(double, double, double );

before you call it.

You should also declare the overload with two parameters version before you use it but you end up picking a version from the standard library. Getting rid of

using namespace std;

should detect that problem as well.

Ron · Answer 3 · 2017-10-30T23:19:28.240

As-is this will not compile. You are introducing the std namespace into a current scope but there will not be a call to std::max on VS implementation while there will be one on Linux GCC implementation, apparently via the stl_algobase.h header:

/usr/local/include/c++/7.2.0/bits/stl_algobase.h: In instantiation of 'constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare) [with _Tp = double; _Compare = double]':

Provide all three function declarations before the main() function:

double max(double, double);
double max(double, double, double);
double max(double, double, double, double);
int main() {
// same as before
}

Live example on Coliru

That being said don't use the using namespace std; statement.

Yes! I didn't declare my 3 parameter overloaded function and tis is why it is not working! Thank you so much! As for the using namespace std; bit, I'm just following along with what my professor said to use I'm sure we will cover it in great detail at a later date ;) — M. Pereira, Oct 30 '17 at 23:17

Trouble with function overloading

3 Answers3