float.h中的C标准库的头文件包含了一组浮点值相关的各种平台相关的常数。这些常量是由ANSI C允许更多的可移植程序提出。之前检查所有的常量，它是很好的理解浮点数是由以下四个元素：

组件

组件说明

S

sign ( +/- )

b

base or radix of the exponent representation, 2 for binary, 10 for decimal, 16 for hexadecimal, and so on...

e

exponent, an integer between a minimum emin and a maximum emax.

p

precision, the number of base-b digits in the significand

上述4个组成部分的基础上，一个浮点将它的值，如下所示：

floating-yiibai=(S)p x beorfloating-yiibai=(+/-)precision x baseexponent

库宏

下面的值是特定于实现定义＃define指令，但这些数值可能没有任何比这里给出低。注意，FLT是指为float类型在所有情况下，DBL是指double番，而LDBL指 long double。

宏

描述

FLT_ROUNDS

Defines the rounding mode for floating yiibai addition and it can have any of the following values:

-1 - indeterminable

0 - toward zero

1 - to nearest

2 - toward positive infinity

3 - toward negative infinity

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.

FLT_MANT_DIG

DBL_MANT_DIG

LDBL_MANT_DIG

These macros define the number of digits in the number (in the FLT_RADIX base).

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.

FLT_MIN_EXP

DBL_MIN_EXP

LDBL_MIN_EXP

These macros define the minimum negative integer value for an exponent in base FLT_RADIX.

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.

FLT_MAX_EXP

DBL_MAX_EXP

LDBL_MAX_EXP

These macros define the maximum integer value for an exponent in base FLT_RADIX.

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.

FLT_MAX 1E+37

DBL_MAX 1E+37

LDBL_MAX 1E+37

These macros define the maximum finite floating-yiibai value.

FLT_EPSILON 1E-5

DBL_EPSILON 1E-9

LDBL_EPSILON 1E-9

These macros define the least significant digit representable.

FLT_MIN 1E-37

DBL_MIN 1E-37

LDBL_MIN 1E-37

These macros define the minimum floating-yiibai value..

例子

下面的例子演示了如何使用几个在float.h文件中定义的常量。

#include#includeintmain(){printf("The maximum value of float = %.10e

",FLT_MAX);printf("The minimum value of float = %.10e

",FLT_MIN);printf("The number of digits in the number = %.10e

",FLT_MANT_DIG);}

让我们编译和运行上面的程序，这将产生以下结果：

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

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