【求解惑】关于“有效数位”与“有效位数”的区别
在cfloat头文件中关于系统的限制有如下：
// the following are the minimum number of significant digits
#define DBL_DIG 15 // double
#define FLT_DIG 6 // float
#define LDBL_DIG 18 // long double
这说的是各种类型的有效数位吧？
而书中又说“C和C++对于有效位数的要求是，float至少32位，double至少48位，且不少于float.”
这里说的有效位数是指的bit还是什么？
[解决办法]
float.h
...
#define DBL_DIG 15 /* # of decimal digits of precision */
#define DBL_EPSILON 2.2204460492503131e-016 /* smallest such that 1.0+DBL_EPSILON != 1.0 */
#define DBL_MANT_DIG 53 /* # of bits in mantissa */
#define DBL_MAX 1.7976931348623158e+308 /* max value */
#define DBL_MAX_10_EXP 308 /* max decimal exponent */
#define DBL_MAX_EXP 1024 /* max binary exponent */
#define DBL_MIN 2.2250738585072014e-308 /* min positive value */
#define DBL_MIN_10_EXP (-307) /* min decimal exponent */
#define DBL_MIN_EXP (-1021) /* min binary exponent */
#define _DBL_RADIX 2 /* exponent radix */
#define _DBL_ROUNDS 1 /* addition rounding: near */
#define FLT_DIG 6 /* # of decimal digits of precision */
#define FLT_EPSILON 1.192092896e-07F /* smallest such that 1.0+FLT_EPSILON != 1.0 */
#define FLT_GUARD 0
#define FLT_MANT_DIG 24 /* # of bits in mantissa */
#define FLT_MAX 3.402823466e+38F /* max value */
#define FLT_MAX_10_EXP 38 /* max decimal exponent */
#define FLT_MAX_EXP 128 /* max binary exponent */
#define FLT_MIN 1.175494351e-38F /* min positive value */
#define FLT_MIN_10_EXP (-37) /* min decimal exponent */
#define FLT_MIN_EXP (-125) /* min binary exponent */
#define FLT_NORMALIZE 0
#define FLT_RADIX 2 /* exponent radix */
#define FLT_ROUNDS 1 /* addition rounding: near */
#define LDBL_DIG DBL_DIG /* # of decimal digits of precision */
#define LDBL_EPSILON DBL_EPSILON /* smallest such that 1.0+LDBL_EPSILON != 1.0 */
#define LDBL_MANT_DIG DBL_MANT_DIG /* # of bits in mantissa */
#define LDBL_MAX DBL_MAX /* max value */
#define LDBL_MAX_10_EXP DBL_MAX_10_EXP /* max decimal exponent */
#define LDBL_MAX_EXP DBL_MAX_EXP /* max binary exponent */
#define LDBL_MIN DBL_MIN /* min positive value */
#define LDBL_MIN_10_EXP DBL_MIN_10_EXP /* min decimal exponent */
#define LDBL_MIN_EXP DBL_MIN_EXP /* min binary exponent */
#define _LDBL_RADIX DBL_RADIX /* exponent radix */
#define _LDBL_ROUNDS DBL_ROUNDS /* addition rounding: near */
...
