[boost] [xpressive] Warning from one compiler but not another.

From: Dick Bridges (dbridges_at_[hidden])
Date: 2006-01-30 12:21:51

One of our compilers is giving a warning and I cannot understand
why.  Maybe I'm missing a #define somewhere?  I don't understand
how the compiler got past the BOOST_MPL_ASSERT_RELATION macros to
even "see" the offending line.

Given the following code:

#include <boost/xpressive/xpressive.hpp>
using namespace boost::xpressive;

int main(int argc, char **argv) {
    sregex re_ = (*_ >> "CALL" >> *_ >> "CONNECTED" >> *_);
    return(0);
}

gcc (GCC) 3.4.4 20050721 (Red Hat 3.4.4-2)
compiles and links successfully with no warnings.

On the other hand, our [arm-softfloat-linux-gnu-gcc
(GCC) 3.3.3] compiler gives the following warnings:

Building file: ../main.cpp
arm-softfloat-linux-gnu-g++ -D_REENTRANT -DARCH=ARM
    -I/usr/local/boost_1_33_1
    -O3 -Wall -c -fmessage-length=0 -Wno-non-virtual-dtor
    -omain.o ../main.cpp
    [snip...snip,snip...snip]
../main.cpp:7:   instantiated from here
/usr/local/boost_1_33_1/boost/xpressive/traits/cpp_regex_traits.hpp:241:
    warning: comparison is always false due to limited range of data
type
/usr/local/boost_1_33_1/boost/xpressive/traits/cpp_regex_traits.hpp:241:
warning: comparison is always false due to limited range of data type
Finished building: ../main.cpp
 
Building target: parse_warning
arm-softfloat-linux-gnu-g++  -o parse_warning     main.o    
Finished building: parse_warning
Build complete for project parse_warning

Here is the "offending" code:

static bool is_newline(Char ch)
        {
            BOOST_MPL_ASSERT_RELATION('\r', ==, L'\r');
            BOOST_MPL_ASSERT_RELATION('\n', ==, L'\n');
            BOOST_MPL_ASSERT_RELATION('\f', ==, L'\f');
241 ==>     return L'\r' == ch || L'\n' == ch || L'\f' == ch
                || (1 < SizeOfChar && (0x2028u == ch || 0x2029u == ch ||
0x85u == ch));
        }

Thanks for your time.  Any assistance you could provide would be greatly
appreciated.

Regards,
Dick Bridges