boost preprocessor bug in 1.49

[sni4ok@…]

this example work incorrect with boost 1.49 on g++ 4.61 with compile flags -std=gnu++0x

#define WRITE_TEST_VALUE(r, data, num, name) std::cout << ", num: " << num << ", name: " << BOOST_PP_STRINGIZE(name);
#define ON_FOREACH_ARGS(ArgsArray, Functor) \

BOOST_PP_LIST_FOR_EACH_I(Functor, , \

BOOST_PP_TUPLE_TO_LIST(BOOST_PP_ARRAY_SIZE(ArgsArray), BOOST_PP_ARRAY_DATA(ArgsArray)))

#define TEST_PP_LIST_FOREACH(ArgsArray) \

std::cout << " sz: " << BOOST_PP_ARRAY_SIZE(ArgsArray); \
ON_FOREACH_ARGS(ArgsArray, WRITE_TEST_VALUE)

#include <iostream>
#include <boost/preprocessor/list.hpp>
#include <boost/preprocessor/tuple.hpp>
#include <boost/preprocessor/array.hpp>
#include <boost/preprocessor/stringize.hpp>

int main()
{

std::cout << "0:" << std::endl;
TEST_PP_LIST_FOREACH((0, ()))
std::cout << std::endl << "1:" << std::endl;
TEST_PP_LIST_FOREACH((1, (bla)))
std::cout << std::endl << "2:" << std::endl;
TEST_PP_LIST_FOREACH((2, (nu, bla)))
std::cout << std::endl;
return 0;

}

output:
g++ test_pp.cpp -I/home/snike/boost/boost_1_49_0
./a.out
0:
sz: 0
1:
sz: 1, num: 0, name: bla
2:
sz: 2, num: 0, name: nu, num: 1, name: bla

output2:
g++ test_pp.cpp -I/home/snike/boost/boost_1_49_0 -std=gnu++0x
./a.out
0:
sz: 0, num: 0, name:
1:
sz: 1, num: 0, name: bla
2:
sz: 2, num: 0, name: nu, num: 1, name: bla

on boost 1.48 this example work correctly

[anonymous]

Yes, the boost preprocessor library changed behavior from 1.48.0 to 1.49.0.

For Visual C++ 8.0, preprocessing this code:

#include <boost/preprocessor/tuple/to_list.hpp>

BOOST_PP_TUPLE_TO_LIST(2, (a, b))
BOOST_PP_TUPLE_TO_LIST(1, (a))
BOOST_PP_TUPLE_TO_LIST(0, ())

used to give this output:

(a, (b, BOOST_PP_NIL))
(a, BOOST_PP_NIL)
BOOST_PP_NIL

but for 1.49.0 the compiler give these warnings:

a.cpp(5) : warning C4003: not enough actual parameters for macro 'BOOST_PP_TUPLE_TO_LIST_1' a.cpp(5) : warning C4003: not enough actual parameters for macro 'BOOST_PP_TUPLE_TO_LIST_1'

and this output:

(a, (b, BOOST_PP_NIL))
(a, BOOST_PP_NIL)
(, BOOST_PP_NIL)

I have similar problems for BOOST_PP_TUPLE_TO_SEQ() and for Clang 3.1. These problems still exist for the latest version of boost (1.52.0).

[anonymous]

These problems are related to this ticket: ​https://svn.boost.org/trac/boost/ticket/7560

[Edward Diener]

There is no such thing as a tuple of size 0. Therefore attempting to pass 0 for a tuple size gives undefined behavior.