I'd like to get a warning for code like this: #include <iostream> using namespace std; int main() { unsigned long four = 400000; unsigned short two; two = four; cout << two << endl; } /home/enadler/test/compilerwarnings $ g++ -Werror -Wall -Wconversion -ansi gccbugreport.cc && a.out 6784 I think GCC is doing the right thing by allowing this code uncasted, and it is described this way in Bjarne's C++ Programming Language, Special Edition C.6.2.1. However, it seems reasonable to me that a warning option should be available to notify the programmer that data is being thrown away. Thanks! Eric
Installed Red Hat Advanced Server 3.0, update 1 Dell PowerEdge 1750: Intel Xeon 2.4GHz Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.3/specs Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux Thread model: posix gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-24)
Confirmed, I thought I saw a bug about this before.
The example given is in C++, not C; the C version is bug 2707.
This will be fixed by the new Wconversion option. Actually, it has been fixed already for gcc version 4.3.0 20061124 (experimental). manuel@gcc05:~$ local/bin/g++ -c -Wconversion pr18821.C pr18821.C: In function ‘int main()’: pr18821.C:8: warning: conversion to ‘short unsigned int’ from ‘long unsigned int’ may alter its value I hope this makes you happy! It is a shame that I missed this bug in the Changelog. Should I modify the Changelog or what is done is done ?
For reference: Author: manu Date: Fri Nov 24 01:50:33 2006 New Revision: 119143 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=119143 Log: 2006-11-24 Manuel Lopez-Ibanez <manu@gcc.gnu.org> PR c/2707 PR c++/26167 * c-common.c (conversion_warning): New. (convert_and_check): Call conversion_warning unless there is an overflow warning. * doc/invoke.texi (-Wconversion): Update description. testsuite/ * gcc.dg/Wconversion-integer.c: New. Supersedes Wconversion-negative-constants.c * gcc.dg/Wconversion-real.c: New. * gcc.dg/Wconversion-real-integer.c: New. * gcc.dg/Wconversion-negative-constants.c: Deleted. * g++.dg/warn/Wconversion1.C: Modified. Added: trunk/gcc/testsuite/gcc.dg/Wconversion-integer.c trunk/gcc/testsuite/gcc.dg/Wconversion-real-integer.c trunk/gcc/testsuite/gcc.dg/Wconversion-real.c Removed: trunk/gcc/testsuite/gcc.dg/Wconversion-negative-constants.c Modified: trunk/gcc/ChangeLog trunk/gcc/c-common.c trunk/gcc/doc/invoke.texi trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/g++.dg/warn/Wconversion1.C