[Bug c++/57170] No diagnostic for a negative case when switching over unsigned
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 TC changed: What|Removed |Added CC||rs2740 at gmail dot com --- Comment #2 from TC --- As comment #0 alluded to - perhaps a bit opaquely - this code is ill-formed in C++11 and later. [stmt.switch] requires the case expression to be "a converted constant expression ([expr.const]) of the promoted type of the switch condition", and a narrowing conversion cannot be used in a converted constant expression. The standard requires a diagnostic, which GCC fails to provide even with -pedantic. (Meanwhile, using unsigned char or unsigned short there is actually well-formed if they get promoted to int as they usually do.) So, unless you are saying that GCC's full conformance mode requires -Wsign-conversion, I don't see how this bug is invalid.
[Bug c++/57170] No diagnostic for a negative case when switching over unsigned
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 Eric Gallager changed: What|Removed |Added Keywords||diagnostic Status|UNCONFIRMED |RESOLVED CC||egallager at gcc dot gnu.org Resolution|--- |INVALID --- Comment #1 from Eric Gallager --- Use -Wsign-conversion to get a warning: $ /usr/local/bin/gcc -c -Wall -Wextra -Wconversion -Wnarrowing -pedantic -Wswitch -Wsign-promo -Wtype-limits -Wsign-conversion -std=c++98 57170.cc 57170.cc: In function ‘int main()’: 57170.cc:4:3: warning: unsigned conversion from ‘int’ to ‘unsigned int’ changes value from ‘-1’ to ‘4294967295’ [-Wsign-conversion] case -1: ^~~~ $ -Wsign-conversion has to be specified explicitly in c++, but in plain c, it's implied by -Wconversion: $ /usr/local/bin/gcc -c -x c -Wall -Wextra -Wconversion -pedantic -Wswitch -Wtype-limits 57170.cc 57170.cc: In function ‘main’: 57170.cc:4:3: warning: unsigned conversion from ‘int’ to ‘unsigned int’ changes value from ‘-1’ to ‘4294967295’ [-Wsign-conversion] case -1: ^~~~ $
