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 be

or

floating-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 <stdio.h>
#include <float.h>

int main()
{
   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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