Detecting the datatype of argument

[a sk]

Hi All - Question from a newbie. I have a print() function that I would like to overload. So, I would like it to work in both scenarios below:

print(string my_string);
print(float ** my_matrix);

How do I detect/identify inside the function, the data type of the argument passed in, especially when it's a pointer to pointer (as in float ** my_matrix)? Once the function knows the data type, it can manage the printing accordingly.

Thanks.

[3qX21hU5]

Just create 2 functions one that accepts a pointer to a pointer of a float as a parameter and one that accepts a string. The compiler will then figure out which one to use by what you pass in as a argument to the function.

For example (I left out the pointer to a pointer stuff so you can figure it out).

void print(const std::string& myString)
{
	std::cout << myString << std::endl;
}

void print(float myFloat)
{
	std::cout << myFloat << std::endl;
}

int main()
{
	print("Hello");   // Will call the string version
	print(1.05);       // Will call the float version
}

[a sk]

Thanks Zereo! Isn't that too much code? Is there way to identify the data type? And probably just use a single function?

[AbstractionAnon]

Isn't that too much code?

That's the way it's done in C++.

And probably just use a single function?

You would still have to pass in another argument indicating the type of the argument to be printed.

[Thumper]

skafetaur wrote:

And probably just use a single function?

Template it.

template<typename T>
void print(T const &rhs)
{
    std::cout << rhs << std::endl;
}

print will work for every data type that cout has an operator<< overload for.

EDIT:
But if you're overloading operator<<, you don't really need another print function.

skafetaur wrote:

Once the function knows the data type, it can manage the printing accordingly.

This is what function overloading was intended for (what Zereo explained in his post)

[a sk]

Thank you Zereo & Thumper.

Leaving aside all of the above, is there way in C++ to detect the data type of an variable (forget functions and overloading), especially a pointer-to-pointer? For instance I could detect an integer or float data type by checking if the variable value is unchanged in upper & lower case (a string containing alpha numeric characters would fail that test).

How do I check if a variable is of type ** (pointer-to-pointer)?

Thanks once again.

[ne555]

> is there way in C++ to detect the data type of an variable
go to its declaration, look at the left

[Thumper]

skafetaur wrote:

How do I check if a variable is of type ** (pointer-to-pointer)?

C++11 introduces decltype and type_traits. (this is a good article: http://www.cprogramming.com/c++11/c++11-auto-decltype-return-value-after-function.html)

Consider the following example:

1 2 3 4 5 6 7 8 9 10 11 12

#include <iostream> #include <iomanip> #include <type_traits> int main() { int **someDoublePointer; std::cout << std::boolalpha << std::is_same<decltype(someDoublePointer), int**>::value << std::endl; }

true

There are a whole bunch of additional functions in type_traits as well. It's worth checking out:
http://www.cplusplus.com/reference/type_traits/

ne555 wrote:

go to its declaration, look at the left

ne555 is right though. There should very rarely be a scenario in C++ where you don't already know the exact type of data you're dealing with.

[a sk]

Thanks again.