VC++ compiler and type conversion?

Question

When I moved a program from a Mac to this Windows PC, the VC++ 2008 compiler is giving me errors for passing unsigned ints to the cmath pow() function. As I understand, this function is not overloaded to accept anything but floating-point numbers.

Is there some compiler flag/setting that will ignore these errors? Also does anyone know how to find the documentation on the VC++ compiler?

Edit

This isn't a warning, it's an error. However, for me it's not an issue since my program is only dealing with numbers that come out as integers, so I don't care that they aren't floats. If it was just warnings I would move on with my life, but it's not letting me compile. Can I suppress errors somehow? Like I said, the errors aren't coming up on my Mac and the program is fine.

Answer 1

Regarding other answers here, it is not a good idea to tell the question author to turn off this warning. His code is broken - he's passing an unsigned int instead of a float. You should be telling him to fix his code!

This isn't a warning, it's an error. However, for me it's not an issue since my program is only dealing with numbers that come out as integers, so I don't care that they aren't floats. If it was just warnings I would move on with my life, but it's not letting me compile. Can I suppress errors somehow? Like I said, the errors aren't coming up on my Mac and the program is fine.

Integers and floats use different representations internally. If you have the same number in an int and a float, the bit pattern inside the storage for them is completely different. You cannot under any circumstances whatsoever expect your code to work if you are passing an integer when you should be passing a float.

Furthermore, I assert your Mac code either is silently using an overloaded version of that function (e.g. you are on that platform compiling with C++) or you believe it works when in fact it is working by chance or is not actually working.

Addendum

No compilers ever written has the ability to turn off errors.

A warning means the compiler thinks you're making a mistake.

An error means the compiler doesn't know what to do.

Answer 2

There are a couple of options:

In C, the solution is simply to cast the ints to doubles:

pow((double)i, (double)j)

In C++, you can do the same, although you should use a C++-style cast:

pow(static_cast<double>(i), static_cast<double>(j))

But a better idea is to use the overload C++ provides:

std::pow(static_cast<double>(i), j);

The base still has to be a floating-point value, but the exponent can be an int at least

The std:: prefix probably isn't necessary (most compilers make the function available in the global namespace as well).

Of course, to access the C++ versions of the function, you have to include the C++ version of the header.

So instead of #include <math.h> you need to #include <cmath>

C++ provides C++ versions of every C header, using this naming convention. If the C header is called foo.h, the C++ version will be cfoo. When you're writing in C++, you should always prefer these versions.

Answer 3

I don't know of a flag, but getting rid of the warnings was easy enough for me. Just double click on each of the warnings in the "Task List" and add the appropriate casting, whether you prefer

(double) my_variable

or

static_cast<double>(my_variable)

I'm guessing if you're getting the ambiguous warning, there are multiple pow functions defined somewhere. It's better to be explicit in my opinion anyway. For what it's worth, my vote goes with the static_cast option.

Answer 4

As Mehrdad mentioned, use the #pragma warning syntax to disable a warning. Documentation is here - http://msdn.microsoft.com/en-us/library/2c8f766e.aspx

I would be inclined to fix the warnings rather than hide them though!

Answer 5

C++ has overloads for pow/powf for int exponents. Heed the warning.

Answer 6

Don't ignore this or any warnings. Fix them. The compiler is your friend, trying to get you to write good code. It's a friend that believes in tough love, but it is your friend.

If you have an unsigned int and need a float, convert your unsigned in to a float.

And the MSDN Library is the documentation for both the VC++ implementation of the language and the IDE itself.