C++: Math function round() does not compile - why?

[Oliver Elphick <olly@lfix.co.uk>]

I am trying to use the math function round() according to the manpage,
but it does not compile.  Can anyone explain why not, please?

This is a C++ app compiled with g++-2.95 (because the target is a Sharp
Zaurus).

According to man 3 round:

NAME
       round, roundf, roundl - round to nearest integer, away from zero

SYNOPSIS
       #include <math.h>

       double round(double x);
       float roundf(float x);
       long double roundl(long double x);

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


The code is:

class OrderImpl : public OrderForm
{
  ...
  double discpc;
  ...
  void calculate_line(int);
  ...
};

#include <math.h>
...
void OrderImpl::calculate_line(int newqty)
{
  double price = atof(TextLabelPrice->text());
  char tmp[20];
  sprintf(tmp, "%.4f", round((double) newqty * price * discpc) / 100.);
  ...
}


The command line and error are:

g++-2.95 -c -pipe -DQWS -fexceptions -fno-rtti -Wall -W -g -std=c99 -I/opt/Qtopia/include -o orderimpl.o orderimpl.cpp
orderimpl.cpp: In method `void OrderImpl::calculate_line(int)':
orderimpl.cpp:84: implicit declaration of function `int round(...)'


-- 
Oliver Elphick                                          olly@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA  92C8 39E7 280E 3631 3F0E  1EC0 5664 7A2F A543 10EA
                 ========================================
   Do you want to know God?   http://www.lfix.co.uk/knowing_god.html