_isnan, _isnanl：判断浮点数为 NAN (不是数，Not a Number)

int _isnan(double x);

int _isnanl(long double x);

#include

std

x：浮点数

≠0: 参数 x 是 NAN

=0: 参数 x 不是 NAN

void __fastcall TForm1::Button1Click(TObject *Sender)

{

double z =  0.0;

double a =  1.0;

double b = -2.0;

UnicodeString s;

s.cat_sprintf(L"%4.1lf/%4.1lf = %4.1lf ; _isnan(%4.1lf) = %d\r\n", a, z, a/z, a/z, std::_isnan(a/z));

s.cat_sprintf(L"%4.1lf/%4.1lf = %4.1lf ; _isnan(%4.1lf) = %d\r\n", b, z, b/z, b/z, std::_isnan(b/z));

s.cat_sprintf(L"%4.1lf/%4.1lf = %4.1lf ; _isnan(%4.1lf) = %d\r\n", z, z, z/z, z/z, std::_isnan(z/z));

s.cat_sprintf(L"%4.1lf/%4.1lf = %4.1lf ; _isnan(%4.1lf) = %d\r\n", a, b, a/b, a/b, std::_isnan(a/b));

Memo1->Lines->Text = s;

}

bcc32

clang32

clang64

_isnan

√

√

√

_isnanl

√

√

√