Return different types using Boost Variant

Here the given program will explain how boost variant  will helpful when there is a situation like, we need to return multiple types. There may be situations like we cannot use templates. In such cases boost variant will be the best solution.

#include <iostream>
#include <string>
#include <boost/variant.hpp>

boost::variant<int,double,std::string> foo(int someValue)
{
    if(0 == someValue)
    {
        return 1;
    }
    else if(someValue < 0)
    {
        return 2.5;
    }
    else
    {
        return "hello";
    }
}

int main()
{
    //In this case the return value is an integer
    boost::variant<int,double,std::string> value1 = foo(0);
    int integerValue = boost::get<int>(value1);

    //In this case the return value is a double
    boost::variant<int,double,std::string> value2 = foo(-1);
    double doubleValue = boost::get<double>(value2);

    //In this case the return value is an std::string
    boost::variant<int,double,std::string> value3 = foo(1);
    std::string stringValue = boost::get<std::string>(value3);

    return 0;
}

Whenever you use boost::variant you should be very careful. If you are C++ beginner like me, definitely you may have a chance get an error message like this

 "terminate called after throwing an instance of 'boost::bad_get'   what():  boost::bad_get: failed value  get using boost::get Aborted (core dumped)"

This is because you need to specifically get (boost::get) the value from boost::variant variable with it's type. If you try to boost::get by wrong type then you will get the above error message.

How to know about type of value inside a boost variant variable

boost::variant<int, double, std::string> someVariable;
someVariable = "Hello World";

"someVariable.which()" will give index of the type as declared in variable. In this case it will give index as 2.