isnan() with gcc 3.2.2 on FreeBSD 5.0-C

the following code snippet works fine with gcc 2.95.4 on RELENG_4
but failed on my -current

<code>
#include <iostream>
#include <cmath>

using namespace std;

int main(void)
{
    cout << isnan(1.0) << endl;
    return 0;
}
</code>

<err>
test.cpp: In function `int main()':
test.cpp:8: `isnan' undeclared (first use this function)
test.cpp:8: (Each undeclared identifier is reported only once for each function
   it appears in.)
</err>

what's wrong with my system ? or what can I do for it ?
-- 
int i;main(){for(;i["]<i;++i){--i;}"];read('-'-'-',i+++"hell\
o, world!\n",'/'/'/'));}read(j,i,p){write(j/p+p,i---j,i/i);}
					-- IOCCC 1984