Catching exception from custom sqrt function fails in C++

Question

I was trying to demonstrate exception handling and came across an oddity I can't solve. The problem arises in the following code:

#include <iostream>
#include <cmath>
#include <stdexcept>

using namespace std;

double sqrt(double x) {                                                         
    if ( x < 0 ){
        throw invalid_argument("sqrt received negative argument");
    }
    return sqrt(x);
}


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

    try {
        double s = sqrt(-1);
    }
    catch (const exception& e) {
        cout << "Caught " << e.what() << endl;
    }
    return 0;
}

The code fails:

 terminate called after throwing an instance of 'std::invalid_argument'
 what():  sqrt received negative argument
 ./dostuff.sh: line 8:  3472 Aborted                 (core dumped) ./may_22.exe

If, however, I either change the name of the sqrt function I write to "mySqrt", or remove the header, the exception is properly caught. Any idea what is causing this?

I'm compiling via

 g++ -g -Wall -std=c++0x -Weffc++   may_22.cpp -o may_22.exe

with g++ (Ubuntu/Linaro 4.8.1-10ubuntu9) 4.8.1

EDIT: To clarify, this does not seem like a namespace issue. The code is clearly calling my sqrt function, as shown by the exception message.

EDIT 2: This code still fails to handle the exception for me.

#include <iostream>
#include <cmath>
#include <stdexcept>

double sqrt(double x) {
    if ( x < 0 ){
        throw std::invalid_argument("sqrt received negative argument");
    }
    return std::sqrt(x);                                                        
}

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

    try {
        double s = sqrt(-1);
    }
    catch (std::exception& e) {
        std::cout << "Caught " << e.what() << std::endl;
    }

    return 0;
}

Answer 1

You just can't call a function sqrt, since that's reserved. Your function is getting called, but your implementation is also including a header file that says that sqrt cannot throw. Change the name of the function to something else and the problem will go away.

You can also see the problem if you change your function to double sqrt(double const& x) {. You'll probably get an error about conflicting overloads.

Answer 2

sqrt() is reserved from the cmath library. Try changing it to double squareRoot(double x). That should at least fix that problem. Sorry, that's all I can help you with.