[Bug libstdc++/15276] New: Erroneous Comparisons of Negative Characters

["mckelvey at maskull dot com" <gcc-bugzilla at gcc dot gnu dot org>]

When chars are implemented as signed, characters with negative values compare 
properly as individual chars, but improperly when part of a char array or 
std::string -- they compare as unsigned. The problem appears to be that the 
specialization of std::char_traits<char> uses memcmp. This is observed on an 
Alpha running RH 7.1 and gcc version 3.5.0 20040207.

Specifically, std::char_traits<char>::compare is inconsistent with 
std::char_traits<char>::lt, which affects std::string (which is just 
std::basic_string<char>.) The problem also affects strcmp, strncmp, and 
strcoll.


Result of running test program, with my analysis:

122      Expected character value of 'z'.
-64      Expected value of signed character '\0300'
192      Expected value of unsigned character '\0300'
-64      Shows that chars are signed

SC 1    Expected character comparison as signed char
UC 0    Expected character comparison as unsigned char
CH 1    Expected character comparison as char (signed)
SV 1    Demonstrates that std::string::value_type is signed
ST 0    Error: std::string of length 1 does not compare the same as CH
BS 1    std::basic_string<signed char> compares as expected
BU 0    std::basic_string<unsigned char> compares as expected
BC 0    Error: Same as ST, as expected (std::basic_string<char>)
TS 1    std::char_traits<signed char> compares signed char * as expected
TU 0    std::char_traits<signed char> compares unsigned char * as expected
TC 0    Error: std::char_traits<char>, char * does not compare properly
LS 1    std::char_traits<signed char> compares signed char as expected
LU 0    std::char_traits<unsigned char> compares unsigned char as expected
LC 1    std::char_traits<char> compares char as expected
          (Note: inconsistent with TC)
MC 0   std::memcmp is comparing as unsigned (I guess that's OK)
SC 0    Error: std::strcmp is comparing as unsigned
SN 0    Error: std::strncmp is comparing as unsigned
SL 0     Error: std::strcoll is comparing as unsigned

-- 
           Summary: Erroneous Comparisons of Negative Characters
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mckelvey at maskull dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: alphaev56-unknown-linux-gnu
  GCC host triplet: alphaev56-unknown-linux-gnu
GCC target triplet: alphaev56-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15276