<float.h> - C語言標準庫

float.h中的C標準庫的頭文件包含了一組浮點值相關的各種平臺相關的常數。這些常量是由ANSI C允許更多的可移植程序提出。之前檢查所有的常量，它是很好的理解浮點數是由以下四個元素：

組件

組件說明

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個組成部分的基礎上，一個浮點將它的值，如下所示：

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

庫宏

下面的值是特定於實現定義＃define指令，但這些數值可能沒有任何比這裏給出低。注意，FLT是指爲float類型在所有情況下，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

下面的例子演示瞭如何使用幾個在float.h文件中定義的常量。

#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); }

讓我們編譯和運行上面的程序，這將產生以下結果：

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