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📅 最后修改于: 2020-12-19 05:37:16 🧑 作者: Mango

C标准库的float.h头文件包含一组与浮点值相关的各种依赖于平台的常量。这些常量由ANSI C提出。它们允许制作更多可移植的程序。在检查所有常量之前，最好了解浮点数由以下四个元素组成：

Sr.No.	Component & Component Description
1	S sign ( +/- )
2	b base or radix of the exponent representation, 2 for binary, 10 for decimal, 16 for hexadecimal, and so on…
3	e exponent, an integer between a minimum e_min and a maximum e_max.
4	p precision, the number of base-b digits in the significand.

基于以上四个组成部分，浮点的值如下：

floating-point = ( S ) p x be

or

floating-point = (+/-) precision x baseexponent

图书馆巨集

以下值为特定于实现的值，并使用#define指令定义，但这些值不得低于此处给出的值。请注意，在所有情况下，FLT表示float类型，DBL表示double类型，而LDBL表示long double类型。

Sr.No.	Macro & Description
1	FLT_ROUNDS Defines the rounding mode for floating point addition and it can have any of the following values − -1 − indeterminable 0 − towards zero 1 − to nearest 2 − towards positive infinity 3 − towards negative infinity
2	FLT_RADIX 2 This defines the base radix representation of the exponent. A base-2 is binary, base-10 is the normal decimal representation, base-16 is Hex.
3	FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG These macros define the number of digits in the number (in the FLT_RADIX base).
4	FLT_DIG 6 DBL_DIG 10 LDBL_DIG 10 These macros define the maximum number decimal digits (base-10) that can be represented without change after rounding.
5	FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP These macros define the minimum negative integer value for an exponent in base FLT_RADIX.
6	FLT_MIN_10_EXP -37 DBL_MIN_10_EXP -37 LDBL_MIN_10_EXP -37 These macros define the minimum negative integer value for an exponent in base 10.
7	FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP These macros define the maximum integer value for an exponent in base FLT_RADIX.
8	FLT_MAX_10_EXP +37 DBL_MAX_10_EXP +37 LDBL_MAX_10_EXP +37 These macros define the maximum integer value for an exponent in base 10.
9	FLT_MAX 1E+37 DBL_MAX 1E+37 LDBL_MAX 1E+37 These macros define the maximum finite floating-point value.
10	FLT_EPSILON 1E-5 DBL_EPSILON 1E-9 LDBL_EPSILON 1E-9 These macros define the least significant digit representable.
11	FLT_MIN 1E-37 DBL_MIN 1E-37 LDBL_MIN 1E-37 These macros define the minimum floating-point values.

例

以下示例显示了float.h文件中定义的几个常量的用法。

现场演示

#include 
#include 

int main () {
   printf("The maximum value of float = %.10e\n", FLT_MAX);
   printf("The minimum value of float = %.10e\n", FLT_MIN);

   printf("The number of digits in the number = %.10e\n", FLT_MANT_DIG);
}

让我们编译并运行上面的程序，它将产生以下结果-

The maximum value of float = 3.4028234664e+38
The minimum value of float = 1.1754943508e-38
The number of digits in the number = 7.2996655210e-312