MIN and MAX in C

Question

Where are MIN and MAX defined in C  if at all   What is the best way to implement these  as generically and type safely as possible   Compiler extensions builtins for mainstream compilers preferred

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Where are MIN and MAX defined in C  if at all    They aren t      What is the best way to implement these  as generically and type safe as possible  compiler extensions builtins for mainstream compilers preferred     As functions  I wouldn t use macros like  define MIN X  Y     X   lt   Y      X     Y    especially if you plan to deploy your code  Either write your own  use something like standard fmax or fmin  or fix the macro using GCC s typeof  you get typesafety bonus too  in a GCC statement expression     define max a b            typeof    a   a    a              typeof    b   b    b           a  gt   b    a    b       Everyone says  oh I know about double evaluation  it s no problem  and a few months down the road  you ll be debugging the silliest problems for hours on end   Note the use of   typeof   instead of typeof      If you are writing a header file that   must work when included in ISO C   programs  write   typeof   instead of   typeof

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This is a late answer  due to a fairly recent development  Since the OP accepted the answer that relies on a non-portable GCC  and clang  extension typeof - or   typeof   for  clean  ISO C - there s a better solution available as of gcc-4 9    define max x y              auto type   x    x     auto type   y    y             x  gt    y     x     y       The obvious benefit of this extension is that each macro argument is only expanded once  unlike the   typeof   solution     auto type is a limited form of C  11 s auto  It cannot  or should not   be used in C   code  though there s no good reason not to use the superior type inference capabilities of auto when using C  11   That said  I assume there are no issues using this syntax when the macro is included in an extern  C          scope  e g   from a C header  AFAIK  this extension has not found its way info clang

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I know the guy said  C     But if you have the chance  use a C   template   template lt class T gt  T min T a  T b    return a  lt  b   a   b      Type safe  and no problems with the    mentioned in other comments

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It s worth pointing out I think that if you define min and max with the ternary operation such as  define MIN a b     a  lt  b    a   b    define MAX a b     a  gt  b    a   b    then to get the same result for the special case of fmin -0 0 0 0  and fmax -0 0 0 0  you need to swap the arguments fmax a b    MAX a b  fmin a b    MIN b a

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It s also provided in the GNU libc  Linux  and FreeBSD versions of sys param h  and has the definition provided by dreamlax   On Debian    uname -sr Linux 2 6 11    cat  etc debian version 5 0 2    egrep  MIN   MAX     usr include sys param h  define MIN a b     a  lt  b    a   b    define MAX a b     a  gt  b    a   b      head -n 2  usr include sys param h   grep GNU This file is part of the GNU C Library   On FreeBSD    uname -sr FreeBSD 5 5-STABLE    egrep  MIN   MAX     usr include sys param h  define MIN a b     a  lt  b    a   b    define MAX a b     a  gt  b    a   b     The source repositories are here   GNU C Library FreeBSD

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I wrote this version that works for MSVC  GCC  C  and C      if defined   cplusplus   amp  amp   defined   GNUC        include  lt algorithm gt      define MIN std  min     define MAX std  max       define TMIN T  a  b  std  min lt T gt  a  b        define TMAX T  a  b  std  max lt T gt  a  b   else         define  CHOOSE2 binoper  lexpr  lvar  rexpr  rvar                                                 decltype lexpr  lvar    lexpr                             decltype rexpr  rvar    rexpr                             lvar binoper rvar   lvar   rvar                               define  CHOOSE VAR2 prefix  unique  prefix  unique         define  CHOOSE VAR prefix  unique   CHOOSE VAR2 prefix  unique          define  CHOOSE binoper  lexpr  rexpr                     CHOOSE2                            binoper                            lexpr   CHOOSE VAR  left    COUNTER                               rexpr   CHOOSE VAR  right    COUNTER                                define MIN a  b   CHOOSE  lt   a  b          define MAX a  b   CHOOSE  gt   a  b   endif

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Looks like Windef h  a la  include  lt windows h gt   has max and min  lower case  macros  that also suffer from the  double evaluation  difficulty  but they re there for those that don t want to re-roll their own

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If you need min max in order to avoid an expensive branch  you shouldn t use the ternary operator  as it will compile down to a jump  The link below describes a useful method for implementing a min max function without branching   http   graphics stanford edu  seander bithacks html IntegerMinOrMax

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The maximum of two integers a and b is  int  0 5  a b  abs a-b     This may also work with  double  and fabs a-b  for doubles  similar for floats

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I don t think that they are standardised macros  There are standardised functions for floating point already  fmax and fmin  and fmaxf for floats  and fmaxl for long doubles    You can implement them as macros as long as you are aware of the issues of side-effects double-evaluation    define MAX a b    a   gt   b    a   b   define MIN a b    a   lt   b    a   b    In most cases  you can leave it to the compiler to determine what you re trying to do and optimise it as best it can  While this causes problems when used like MAX i    j     I doubt there is ever much need in checking the maximum of incremented values in one go  Increment first  then check

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There s a std  min and std  max in C    but AFAIK  there s no equivalent in the C standard library   You can define them yourself with macros like   define MAX x  y     x   gt   y      x     y    define MIN x  y     x   lt   y      x     y     But this causes problems if you write something like MAX   a    b

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The simplest way is to define it as a global function in a  h file  and call it whenever you want  if your program is modular with lots of files  If not  double MIN a b  return  a lt b a b   is the simplest way

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Avoid non-standard compiler extensions and implement it as a completely type-safe macro in pure standard C  ISO 9899 2011    Solution   define GENERIC MAX x  y    x   gt   y     x     y     define ENSURE int i     Generic  i   int     i    define ENSURE float f   Generic  f   float   f      define MAX type  x  y       type GENERIC MAX ENSURE   type x   ENSURE   type y     Usage   MAX int  2  3      Explanation  The macro MAX creates another macro based on the type parameter  This control macro  if implemented for the given type  is used to check that both parameters are of the correct type  If the type is not supported  there will be a compiler error   If either x or y is not of the correct type  there will be a compiler error in the ENSURE  macros  More such macros can be added if more types are supported  I ve assumed that only arithmetic types  integers  floats  pointers etc  will be used and not structs or arrays etc   If all types are correct  the GENERIC MAX macro will be called  Extra parenthesis are needed around each macro parameter  as the usual standard precaution when writing C macros   Then there s the usual problems with implicit type promotions in C  The   operator balances the 2nd and 3rd operand against each other  For example  the result of GENERIC MAX my char1  my char2  would be an int  To prevent the macro from doing such potentially dangerous type promotions  a final type cast to the intended type was used   Rationale  We want both parameters to the macro to be of the same type  If one of them is of a different type  the macro is no longer type safe  because an operator like    will yield implicit type promotions  And because it does  we also always need to cast the final result back to the intended type as explained above   A macro with just one parameter could have been written in a much simpler way  But with 2 or more parameters  there is a need to include an extra type parameter  Because something like this is unfortunately impossible      this won t work  define MAX x  y                                        Generic  x                                                   int  GENERIC MAX x  ENSURE int y                     float  GENERIC MAX x  ENSURE float y                    The problem is that if the above macro is called as MAX 1  2  with two int  it will still try to macro-expand all possible scenarios of the  Generic association list  So the ENSURE float macro will get expanded too  even though it isn t relevant for int  And since that macro intentionally only contains the float type  the code won t compile   To solve this  I created the macro name during the pre-processor phase instead  with the    operator  so that no macro gets accidentally expanded   Examples   include  lt stdio h gt    define GENERIC MAX x  y    x   gt   y     x     y     define ENSURE int i     Generic  i   int     i    define ENSURE float f   Generic  f   float   f      define MAX type  x  y       type GENERIC MAX ENSURE   type x   ENSURE   type y    int main  void      int    ia   1     ib   2    float  fa   3 0f  fb   4 0f    double da   5 0   db   6 0     printf   d n   MAX int    ia  ib       ok   printf   f n   MAX float  fa  fb       ok    printf   d n   MAX int    ia  fa     compiler error  one of the types is wrong   printf   f n   MAX float  fa  ib     compiler error  one of the types is wrong   printf   f n   MAX double  fa  fb    compiler error  the specified type is wrong   printf   f n   MAX float  da  db     compiler error  one of the types is wrong    printf   d n   MAX unsigned int  ia  ib       wont get away with this either   printf   d n   MAX int32 t  ia  ib       wont get away with this either   return 0

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Old GCC Extension  Operators  lt     gt     lt      gt    In a very old version of GCC there were the operators  lt     gt    see here  here it was in C   but I think it also applied as a C extension back then  I have also seen the operators  lt      gt    corresponding to the assignment statements  The operands were evaluated once and even allowed for a very short assignment statement  Its very short compared to common min max assignments  There is nothing that can top this  Those were a shorthand for the following  min a  b          a  lt  b   a   b         a  lt   b  max a  b          a  gt  b   a   b         a  gt   b  a   min a  b           if b  lt  a  a   b          a  lt    b  a   max a  b           if b  gt  a  a   b          a  gt    b   Finding the minimum is very concise  int find min const int  ints  int num ints        assert num ints  gt  0       int min   ints 0       for int i   1  i  lt  num ints    i          min  lt    ints i       return min     I hope this might be some day brought back to GCC  because I think these operators are genious

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David Titarenco nailed it here  but let me at least clean it up a bit to make it look nice  and show both min   and max   together to make copying and pasting from here easier       Update 25 Apr  2020  I ve also added a Section 3 to show how this would be done with C   templates too  as a valuable comparison for those learning both C and C    or transitioning from one to the other  I ve done my best to be thorough and factual and correct to make this answer a canonical reference I can come back to again and again  and I hope you find it as useful as I do   1  The old C macro way   This technique is commonly used  well-respected by those who know how to use it properly  the  de facto  way of doing things  and fine to use if used properly  but buggy  think  double-evaluation side effect  if you ever pass expressions including variable assignment in to compare    define MAX a b    a   gt   b     a     b    define MIN a b    a   lt   b     a     b     2  The new and improved gcc  statement expression  way   This technique avoids the above  double-evaluation  side effects and bugs  and is therefore considered the superior  safer  and  more modern  GCC C way to do this  Expect it to work with both the gcc and clang compilers  since clang is  by design  gcc-compatible  see the clang note at the bottom of this answer    BUT  DO watch out for  variable shadowing  effects still  as statement expressions are apparently inlined and therefore do NOT have their own local variable scope    define max a b                                                     typeof    a   a    a           typeof    b   b    b          a  gt   b    a    b               define min a b                                                     typeof    a   a    a           typeof    b   b    b          a  lt   b    a    b               Note that in gcc statement expressions  the last expression in the code block is what is  returned  from the expression  as though it was returned from a function  GCC s documentation says it this way       The last thing in the compound statement should be an expression followed by a semicolon  the value of this subexpression serves as the value of the entire construct   If you use some other kind of statement last within the braces  the construct has type void  and thus effectively no value     3  The C   template way   C   Note  if using C    templates are probably recommended for this type of construct instead  but I personally dislike templates and would probably use one of the above constructs in C   anyway  as I frequently use and prefer C styles in embedded C   as well   This section added 25 Apr  2020     I ve been doing a ton of C   the past few months  and the pressure to prefer templates over macros  where able  in the C   community is quite strong  As a result  I ve been getting better at using templates  and want to put in the C   template versions here for completeness and to make this a more canonical and thorough answer   Here s what basic function template versions of max   and min   might look like in C     template  lt typename T gt  T max T a  T b        return a  gt  b   a   b     template  lt typename T gt  T min T a  T b        return a  lt  b   a   b      Do additional reading about C   templates here  Wikipedia  Template  C      However  both max   and min   are already part of the C   standard library  in the  lt algorithm gt  header   include  lt algorithm gt     In the C   standard library they are defined slightly differently than I have them above  The default prototypes for std  max lt  gt    and std  min lt  gt     for instance  in C  14  looking at their prototypes in the cplusplus com links just above  are   template  lt class T gt   constexpr const T amp  max const T amp  a  const T amp  b    template  lt class T gt   constexpr const T amp  min const T amp  a  const T amp  b     Note that the keyword typename is an alias to class  so their usage is identical whether you say  lt typename T gt  or  lt class T gt    since it was later acknowledged after the invention of C   templates  that the template type might be a regular type  int  float  etc   instead of only a class type   Here you can see that both of the input types  as well as the return type  are const T amp   which means  constant reference to type T   This means the input parameters and return value are passed by reference instead of passed by value  This is like passing by pointers  and is more efficient for large types  such as class objects  The constexpr part of the function modifies the function itself and indicates that the function must be capable of being evaluated at compile-time  at least if provided constexpr input parameters   but if it cannot be evaluated at compile-time  then it defaults back to a run-time evaluation  like any other normal function    The compile-time aspect of a constexpr C   function makes it kind-of C-macro-like  in that if compile-time evaluation is possible for a constexpr function  it will be done at compile-time  same as a MIN   or MAX   macro substitution could possibly be fully evaluated at compile-time in C or C   too  For additional references for this C   template info  see below   References    https   gcc gnu org onlinedocs gcc Typeof html Typeof https   gcc gnu org onlinedocs gcc Statement-Exprs html Statement-Exprs MIN and MAX in C Additional C   template references added Apr  2020         Wikipedia  Template  C     lt -- GREAT additional info about C   templates   My own question  amp  answer   Why is  constexpr  part of the C  14 template prototype for  std  max     Difference between  constexpr  and  const     Clang note from Wikipedia       Clang  is designed to act as a drop-in replacement for the GNU Compiler Collection  GCC   supporting most of its compilation flags and unofficial language extensions

[c] MIN and MAX in C

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