minimum double value in C C

Question

Is there a standard and or portable way to represent the smallest negative value  e g  to use negative infinity  in a C     program   DBL MIN in float h is the smallest positive number

User · Answer

If you do not have float exceptions enabled (which you shouldn't imho), you can simply say:

double neg_inf = -1/0.0;

This yields negative infinity. If you need a float, you can either cast the result

float neg_inf = (float)-1/0.0;

or use single precision arithmetic

float neg_inf = -1.0f/0.0f;

The result is always the same, there is exactly one representation of negative infinity in both single and double precision, and they convert to each other as you would expect.

User · Answer

Try this   -1   numeric limits lt double gt   max     Reference  numeric limits     This class is specialized for each of   the fundamental types  with its   members returning or set to the   different values that define the   properties that type has in the   specific platform in which it   compiles

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Is there a standard and or portable way to represent the smallest negative value  e g  to use negative infinity  in a C     program    C  approach   Many implementations support   - infinities  so the most negative double value is -INFINITY    include  lt math h gt  double most negative   -INFINITY         Is there a standard and or portable way         Now we need to also consider other cases    No infinities   Simply -DBL MAX    Only an unsigned infinity    I d expect in this case  OP would prefer -DBL MAX    De-normal values greater in magnitude than DBL MAX    This is an unusual case  likely outside OP s concern   When double is encoded as a pair of a floating points to achieve desired range precession   see double-double  there exist a maximum normal double and perhaps a greater de-normal one   I have seen debate if DBL MAX should refer to the greatest normal  of the greatest of both   Fortunately this paired approach usually includes an -infinity  so the most negative value remains -INFINITY     For more portability  code can go down the route      HUGE VAL is designed to be infinity or DBL MAX  when infinites are not implemented        yet is problematic with unsigned infinity  double most negative1   -HUGE VAL        Fairly portable  unless system does not understand  INF  double most negative2   strtod  -INF    char     NULL       Pragmatic double most negative3   strtod  -1 0e999999999    char     NULL       Somewhat time-consuming double most negative4   pow -DBL MAX  0xFFFF    odd value          My suggestion double most negative5    -DBL MAX  DBL MAX

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- std  numeric limits lt double gt   max     should work just fine  Numeric limits

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Floating point numbers  IEEE 754  are symmetrical  so if you can represent the greatest value  DBL MAX or numeric limits lt double gt   max     just prepend a minus sign   And then is the cool way   double f      long long   amp f      1LL lt  lt 52

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-DBL MAX in ANSI C  which is defined in float h

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The original question concerns infinity  So  why not use   define Infinity    double  42   0 0     according to the IEEE definition  You can negate that of course

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A truly portable C   solution As from C  11 you can use  numeric limits lt double gt   lowest    According to the standard  it returns exactly what you re looking for   A finite value x such that there is no other finite value y where y  lt  x   Meaningful for all specializations in which is bounded    false   Online demo  Lots of non portable C   answers here   There are many answers going for -std  numeric limits lt double gt   max    Fortunately  they will work well in most of the cases   Floating point encoding schemes decompose a number in a mantissa and an exponent and most of them  e g  the popular IEEE-754  use a distinct sign bit  which doesn t belong to the mantissa  This allows to transform the largest positive in the smallest negative just by flipping the sign   Why aren t these portable   The standard doesn t impose any floating point standard  I agree that my argument is a little bit theoretic  but suppose that some excentric compiler maker would use a revolutionary encoding scheme with a  mantissa encoded in some variations of a two s complement  Two s complement encoding are not symmetric   for example for a signed 8 bit char the maximum positive is 127  but the minimum negative is -128  So we could imagine some floating point encoding show similar asymmetric behavior  I m not aware of any encoding scheme like that  but the point is that the standard doesn t guarantee that the sign flipping yields the intended result   So this popular answer  sorry guys    can t be considered as fully portable standard solution       at least not if you didn t assert that numeric limits lt double gt   is iec559 is true

User · Answer

Are you looking for actual infinity or the minimal finite value  If the former  use  -numeric limits lt double gt   infinity     which only works if  numeric limits lt double gt   has infinity   Otherwise  you should use  numeric limits lt double gt   lowest     which was introduces in C  11   If lowest   is not available  you can fall back to  -numeric limits lt double gt   max     which may differ from lowest   in principle  but normally doesn t in practice

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In C  use   include  lt float h gt   const double lowest double   -DBL MAX    In C  pre-11  use   include  lt limits gt   const double lowest double   -std  numeric limits lt double gt   max      In C  11 and onwards  use   include  lt limits gt   constexpr double lowest double   std  numeric limits lt double gt   lowest

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