Using numeric_limits to default parameter values

Question

I have a template statistics class that has range parameters.

template <typename T>
class limitStats
{
public:
    limitStats(T mx, T min) :
      max(mx),
      min(mn),
      range(mx-mn)
    {;}

private:
    const T max;
    const T min;
    const T range;
}

I would like to put default values of maximum and minimum allowable values, but the minimum value is not the same for floating point and integer types.

Normally I can write

T min_val = numeric_limits<T>::isinteger ? numeric_limits<T>::min() : -numeric_limits<T>::max();

I have found that I can't use it as a default parameter

limitStats(T mx = std::numeric_limts<T>::max(), 
           T mn = numeric_limits<T>::isinteger ? numeric_limits<T>::min() : -numeric_limits<T>::max())

Is there a way of achieving something like this?

David Hammen · Accepted Answer · 2011-07-21 12:20:35Z

You might want to rethink your design. What are you trying to do with your limitStats that std::numeric_limits doesn't provide?

Don't replicate the badness of the design of std::numeric_limits. For example, std::numeric_limits<double>::min() is terribly misnamed. The minimum double is the additive inverse of the maximum double. std::numeric_limits is an abuse of notation and an abuse of templates. In my opinion, of course.

Your idea for min is ill-formed. Think about your default with respect to limitStats<unsigned int>.

With the defaults, your range is invalid for signed integers. For unsigned ints it replicates max, assuming you fix the problem with limitStats<unsigned int>::min. For floating point types, it is either invalid or replicates max, depending on what you mean by limitStats<floating_point_type>::min.

Does it even make sense to allow default values? You wouldn't even have this question if you simply don't provide defaults and make the default constructor private/unimplemented.

visitor · Accepted Answer · 2011-07-21 12:04:57Z

2

There are so many syntax errors and typos that it is hard to tell which of those is your problem.

numeric_limits is a template, so you access it as numeric_limits<int>::is_integer or with a template type numeric_limits<T>::max().

answered Jul 21, 2011 at 12:04

visitor

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Comments

Andrew Stein · Accepted Answer · 2011-07-21 11:58:39Z

1

Use

boost::numeric::bounds<T>::lowest()

See http://www.boost.org/doc/libs/1_33_1/libs/numeric/conversion/doc/bounds.html

answered Jul 21, 2011 at 11:58

Andrew Stein

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1 Comment

Bo Persson Over a year ago

This will appear in C++0x as well, as std::numeric_limits<T>::lowest().

Atul Kumar · Accepted Answer · 2015-04-19 20:28:36Z

I just hit the same issue when trying to have a function signature like below in Windows on Visual studio while trying to create a DLL

int
GetARandomNum(
    int lowest = std::numeric_limits<int>::min(),
    int highest = std::numeric_limits<int>::max());

When trying various stuff, I decided to remove #inlcude <windows.h> from stdafx.h and things started building fine. Given that 'stdafx.h' is selected by default in VS and not including it or not does not make any difference to build error, I decided to simply move #inlcude <windows.h> from stdafx'h to cpp files wherever its needed which in case of a DLL project is usually in dllmain.cpp only. I do not know why Windows.h is messing with C+11 headers but I have seen similar issue earlier also.

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