Wireshark mailing list archives
Re: Making gcc less pedantic
From: Guy Harris <guy () alum mit edu>
Date: Fri, 13 Feb 2015 15:00:49 -0800
On Feb 13, 2015, at 12:54 PM, Gerald Combs <gerald () wireshark org> wrote:
Would it make sense to make gcc's "-pedantic" warnings a bit less pedantic, e.g. with "-std=c99"?
C90 says A bit-field shall have a type that is a qualified or unqualified version of one of int, unsigned int, or signed int. Whether the high-order bit position of a (possibly qualified) “plain” int bit-field is treated as a sign bit is implementation-defined. A bit-field is interpreted as an integral type consisting of the specified number of bits. in 6.5.2.1 "Structure and union specifiers". C99 says A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed int, unsigned int, or some other implementation-defined type. in 6.7.2.1 "Structure and union specifiers". At least as I read C99's 6.2.5 "Types", an enumeration is not any of the specified types, so it would be implementation-defined whether an enumeration is a valid type for a bit-field. So -std=c99 combined with -pedantic does *not* suppress the warning: $ gcc -pedantic -std=c99 enum.c enum.c:4:7: warning: type of bit-field ‘twobits’ is a GCC extension [-Wpedantic] enum frobozz twobits:2; when compiling enum frobozz { red, green, blue }; struct foo { enum frobozz twobits:2; int hello; }; int main(void) { return 0; } -std=cXX, by itself, does *not* cause warnings when features not in cXX are used; to quote the man page: ... When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, such as the "asm" and "typeof" keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a "?:" expression. so even -std=c89 prints no "a bit-field is an enum" warning when used without -pedantic.
In this particular case having a "packet_char_enc" encoding instead of an "unsigned int" encoding is useful, otherwise you have to cast back to packet_char_enc further down the line. It also compiles under Clang, Visual C++, and Solaris Studio without warning.
In practice, I suspect few if any C compilers would refuse to allow enumerations as bit-fields. ___________________________________________________________________________ Sent via: Wireshark-dev mailing list <wireshark-dev () wireshark org> Archives: http://www.wireshark.org/lists/wireshark-dev Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev mailto:wireshark-dev-request () wireshark org?subject=unsubscribe
Current thread:
- Making gcc less pedantic Gerald Combs (Feb 13)
- Re: Making gcc less pedantic Evan Huus (Feb 13)
- Re: Making gcc less pedantic Guy Harris (Feb 13)