Why is sqrt working without cmath?

[nile12]

Why does this programn work without cmath? The code works fine. I was playing around and thought cmath was necessary. However, the code works the same without it.

#include <iostream>
//#include <cmath>
#include <Windows.h>
using namespace std;

// Function Prototype
double sqrRoot(double);

int main()
{
	double num, result;

	cout << "Enter a number and this program\n"
		<< "will return its square root: ";
	cin >> num;

	try 
	{
		result = sqrRoot(num);
		cout << "The square root of " << num << " is " << result << endl;
	}

	catch (const char *exceptionString)
	{
		cout << exceptionString;
	}
	cout << "End of program.\n";
	system("pause");
	return 0;
}


double sqrRoot(double num)
{
	if (num <= 0 || sqrt(num) != static_cast<int>(sqrt(num)))
		throw "Error: The number is not a perfect square.\n";

	return sqrt(num);
}

[edge6768]

Look inside of windows.h, I imagine cmath is included as a child header in it or one of its #includes. I'm on Unix so I don't have a copy of it but an easy way to find out if that's the case would be to comment out #include <Window.h> and see if it still compiles.

[JLBorges]

> Why does this programn work without cmath?

A standard C ++ header may include other standard C++ headers (either in full or in part). In this particular implementation, the declaration of at least one of the overloads of std::sqrt was present in some header included by <iostream> http://rextester.com/HOB4139


> I was playing around and thought cmath was necessary.

It is necessary.

The entities in the C ++ standard library are defined in headers, whose contents are made available to a translation unit when it contains the appropriate #include preprocessing directive

On some implementations, we may get an error: http://coliru.stacked-crooked.com/a/efb18dbf64b3cab7

Even in the case where it appeared to work, all the overloads of std::sqrt() need not be visible; we may not always be calling the overload that would have been called had we included <cmath>

[nile12]

Okay thank you JLBorges. That makes perfect sense. edge6768 Windows.h would not, respectively, have anything to do with sqrt. Thank you both for the response.