请教isnan()和dot_product()两个函数的用法，最好举个例子说说！

在看其他的代码时遇见的，但是查过它们应该时c语言里的！
劳烦各位高手！！非常感谢！

man isnan dot_product

SYNOPSIS
#include <math.h>

int fpclassify(x);

int isfinite(x);

int isnormal(x);

int isnan(x);

int isinf(x);

Compile with -std=c99; link with -lm.

DESCRIPTION
Floating point numbers can have special values, such as infinite or
NaN. With the macro fpclassify(x) you can find out what type x is. The
macro takes any floating-point expression as argument. The result
takes one of the following values:

FP_NAN x is "Not a Number".

FP_INFINITE
x is either plus or minus infinity.

FP_ZERO
x is zero.

FP_SUBNORMAL
x is too small to be represented in normalized format.

FP_NORMAL
if nothing of the above is correct that it must be a normal
floating-point number.

The other macros provide a short answer to some standard questions.
isfinite(x)
returns a non-zero value if
(fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)

isnormal(x)
returns a non-zero value if (fpclassify(x) == FP_NORMAL)

isnan(x)
returns a non-zero value if (fpclassify(x) == FP_NAN)

isinf(x)
returns 1 if x is positive infinity, and -1 if x is negative
infinity.

$man dot_product
No manual entry for dot_product

哇哇！全英文！不过还是谢谢了！我会尽力搞懂的！
thank you very much!!