Why does math.h not declare function round?

["Plato" <zhangguoqiang@xunlei.com>]

Hi!
    I made such a program foo.c:

#include <math.h>

int main()
{
    double bar=1.2;
    printf("%f\n", round(bar));
}
    
Then compile and run:
[root@so41 tmp]# gcc foo.c -ofoo -lm
[root@so41 tmp]# ./foo
0.000000

The result was obviously wrong. Then I add statement:
#include <math.h>
double round(double x);

int main()
{
    double bar=1.2;
    printf("%f\n", round(bar));
}

Then compile and run:
[root@so41 tmp]# gcc foo.c -ofoo -lm
[root@so41 tmp]# ./foo
1.000000

Now it's right.

I wonder why function round not declared in math.h. Anyone have idea?

Thx.




Plato
2007-09-24