Standard C++ Library Reference ISO/IEC (VERSION3)

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<float.h>
Include the standard header <float.h> to determine various properties of floating-point type
representations. The standard header <float.h> is available even in a freestanding
implementation.
You can test only the value of the macro FLT_RADIX in an if directive. All other macros
defined in this header expand to expressions whose values can be determined only when the
program executes. (These macros are rvalue expressions.)
Some target environments can change the rounding and error-reporting properties of
floating-point type representations while the program is running.
#define FLT_RADIX <#if expression >= 2>
#define FLT_ROUNDS <integer rvalue>
#define DBL_DIG <integer rvalue >= 10>
#define DBL_EPSILON <double rvalue <= 10^(-9)>
#define DBL_MANT_DIG <integer rvalue>
#define DBL_MAX <double rvalue >= 10^37>
#define DBL_MAX_10_EXP <integer rvalue >= 37>
#define DBL_MAX_EXP <integer rvalue>
#define DBL_MIN <double rvalue <= 10^(-37)>
#define DBL_MIN_10_EXP <integer rvalue <= -37>
#define DBL_MIN_EXP <integer rvalue>
#define FLT_DIG <integer rvalue >= 6>
#define FLT_EPSILON <float rvalue <= 10^(-5)>
#define FLT_MANT_DIG <integer rvalue>
#define FLT_MAX <float rvalue >= 10^37>
#define FLT_MAX_10_EXP <integer rvalue >= 37>
#define FLT_MAX_EXP <integer rvalue>
#define FLT_MIN <float rvalue <= 10^(-37)>
#define FLT_MIN_10_EXP <integer rvalue <= -37>
#define FLT_MIN_EXP <integer rvalue>
#define LDBL_DIG <integer rvalue >= 10>
#define LDBL_EPSILON <long double rvalue <= 10^(-9)>
#define LDBL_MANT_DIG <integer rvalue>