Home > C++ > std::min and std::max [zz]

std::min and std::max [zz]

This is a repost from blog of Heifner

Today I typed the following:

int t = (std::max)(timeout, lagtime);


Why did I put parentheses around std::max? Because windows.h defines (among other things) a max and a min macro. If you include windows.h the above code will not compile. For example the following:

#include "windows.h"
#include <algorithm>

void foo() {
    int i = 5;
    int j = 7;
    int x = std::max(i,j);
}


Will produce the following error with Visual Studio C++ 2005:

1>test.cpp(7) : error C2589: '(' : illegal token on right side of '::'
1>test.cpp(7) : error C2143: syntax error : missing ';' before '::'


There are a number of ways to work around windows.h defining these two macros. 

    • Use alternative names defined in windows.h.
      int x = _cpp_max(i,j);
      int y = _cpp_min(i,j);

      This is not portable; only works on Windows.

    • Define NOMINMAX before including windows.h. This might break existing code that assumes NOMINMAX is not defined.
    • Don’t use std::min and std::max. Instead use the tertiary operator like so:
      int x = i > j ? i : j; // max(i,j)
      int y = i < j ? i : j; // min(i,j)

      This is portable but not as readable and more error prone.

    • Use using statements to make the code portable:
      using std::min;
      using std::max;
      int x = max(i,j);
      int y = min(i,j);

      This works but requires two more lines of code. You could also just use ‘using namespace std;’ but that might pull in more than you want.

    • Use std::min<int> and std::max<int>
      int x = std::max<int>(i,j);
      int y = std::min<int>(i,j);

      This requires you to specify the type. However in some cases this actually helps. For example:

      int i = 5;
      unsigned int j = 7;
      int x = (std::max)(i,j);
      int y = (std::min)(i,j);

      Note the ‘unsigned’. Generates the following errors:

      1>test.cpp(7) : error C2780: 'const _Ty &std::max(const _Ty &,const _Ty &,_Pr)' :
      expects 3 arguments - 2 provided
      1>        c:\program files\microsoft visual studio 8\vc\include\xutility(3190) :
      see declaration of 'std::max'
      1>test.cpp(7) : error C2782: 'const _Ty &std::max(const _Ty &,const _Ty &)' :
      template parameter '_Ty' is ambiguous
      1>        c:\program files\microsoft visual studio 8\vc\include\xutility(3182) :
      see declaration of 'std::max'
      1>        could be 'unsigned int'
      1>        or 'int'

      By explicitly specifying type via <int> you remove the ambiguity.

  • Use (std::min) and (std::max)
    int i = 5;
    int j = 7;
    int x = (std::max)(i,j);
    int y = (std::min)(i,j);

    This works (as does the std::max<int>) because the C++ preprocessor requires ‘(‘ as the next preprocessing token following the macro name to preform the macro expansion.

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