A number in VMD, herafter called a 'v-number', is a preprocessing 'pp-number', limited to a Boost PP number. This is an integral literal between 0 and 256. The form of the number does not contain leading zeros. Acceptable as v-numbers are:

0
127
33
254
18

but not:

033
06
009
00

As can be seen from the explanation of a v-identifier, a v-number is merely a small subset of all possible v-identifiers, for which VMD internally provides key-identifier macros to test. Therefore the particular constraint on the input to test is exactly the same as for v-identifiers.

The constraint is that the beginning input character, ignoring any whitespace, passed as the input to test must be either:

If this is not the case a preprocessing error will occur.

Given the input:

s_anything : can be tested
S_anything : can be tested
s_anYthiNg : can be tested
s&_anYthiNg : can be tested
_anything : can be tested
_Anything : can be tested
_anytH?Ing : can be tested
24 : can be tested
245e2: can be tested
(anything) : can be tested, tuple
(anything) anything : can be tested, tuple + identifier

%_anything : will give a preprocessing error due to the constraint
(_anything : will give a preprocessing error due to the constraint, since a single '(' does not form a tuple

The macro used to test for a particular v-number in VMD is called BOOST_VMD_IS_NUMBER. The macro takes a single parameter, the input to test against.

The macro returns 1 if the parameter is a Boost PP number, otherwise the maco returns 0.

Example

Let us look at an example of how to use BOOST_VMD_IS_NUMBER.

BOOST_VMD_IS_NUMBER(input)

returns:

if input = 0, 1
if input = 44, 1
if input = SQUARE, 0
if input = 44 DATA, 0 since there are tokens after the number
if input = 044, 0 since no leading zeros are allowed for our Boost PP numbers
if input = 256, 1
if input = 257, 0 since it falls outside the Boost PP number range
if input = %44, does not meet the constraint therefore a preprocessing error occurs
if input = 44.0, 0 since the number is a floating point literal
if input = ( 44 ), 0 since the macro begins with a tuple and this can be tested for

Example

To use the BOOST_VMD_IS_NUMBER macro either include the general header:

#include <boost/vmd/vmd.hpp>

or include the specific header:

#include <boost/vmd/is_number.hpp>