Hi,
I think that this is a FreeBSD issue. I compiled the same file under Linux, with a GCC 3.3.1 checked out on 7/11 and did not encounter this warning.
I think you hit it on the head.
I looked in the source code of gcc and found this: /usr/src/contrib/gcc/c-common.c
2597 case LT_EXPR:
2598 if (extra_warnings && !in_system_header
2599 && ! (TREE_CODE (primop0) == INTEGER_CST
2600 && ! TREE_OVERFLOW (convert (c_common_signed_typ
e (type),
2601 primop0))))
2602 warning ("comparison of unsigned expression < 0 is alway
s false");
2603 value = boolean_false_node;
2604 break;
I am guessing that the C preprocessor does not think that it is in a system header, and thus prints out the warning.
If I take the following preprocessed source (test.ii) and compile it under FreeBSD with g++ -W -c test.ii:
======================================================================= ========
# 1 "test.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.cc"
# 1 "/usr/include/c++/3.3/iostream" 1 3
# 43 "/usr/include/c++/3.3/iostream" 3
static const int digits = (sizeof(unsigned int) * 8 - ((unsigned int)(-1) < 0));
======================================================================= ========
I get:
In file included from test.cc:1:
/usr/include/c++/3.3/iostream:44: warning: comparison of unsigned expression <
0 is always false
If I compile the same file on my Linux box, with a gcc checked out from the FSF CVS repository (gcc version 3.3.1 20030711 (prerelease)), I do not get the warning.
I am not an expert on the GNU C preprocessor format, but I changed two of the lines in the above file to:
# 1 "/usr/include/c++/3.3/iostream" 1 # 43 "/usr/include/c++/3.3/iostream"
and when I recompiled it under Linux, I also got the warning:
In file included from test.cc:1:
/usr/include/c++/3.3/iostream:44: warning: comparison of unsigned expression <
0 is always false
Any GCC/FreeBSD expert care to comment? ;)
-- Craig Rodrigues http://crodrigues.org [EMAIL PROTECTED]
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