Comments on: Warnings I turn on, and why

By: Peter Hosey

Peter Hosey — Wed, 21 Dec 2011 22:32:08 +0000

Conor: There's currently no good solution. However, a future version of Clang (actually the current version, but yet to be included with a release of Xcode) will include a solution originally from C++: typedef enum : unsigned char { Red, Green, Blue } Color; Presumably, you'll be able to use NSUInteger in the middle there as the base type. It's listed on the Clang language extensions page.

By: Conor

Conor — Wed, 21 Dec 2011 11:02:22 +0000

I can’t get past the first example “checking switch statement” for lack of examples on how to write the enum. How do I declare an enum to be able to type check but also keep it compatible with 32-64 bit conversions as required by Apple? The following example below of what I use in my projects requires enums to be anonymous and hence all switches would require a default to avoid the warning.

enum {
NSNullCellType = 0,
NSTextCellType = 1,
NSImageCellType = 2
};
typedef NSUInteger NSCellType;

By: Mark Aufflick

Mark Aufflick — Thu, 19 May 2011 06:54:52 +0000

The implicit 32 to 64 bit conversion warning triggers on constants in recent gcc/clang versions. This requires putting an f after every inline eg. CGFloat literal. This isn’t such a big deal, except when you\’re importing external code you don’t want to fork.

Instead you can add -fsingle-precision-constant as a compiler flag – that will effectively treat all literals as 32 bit. I don’t know about you, but I’ve never had time to type a 64 bit value by hand!

By: Peter Hosey

Peter Hosey — Wed, 16 Feb 2011 23:31:10 +0000

Otto: It does, but it generally will be the right sequence of bytes—most functions will do the right thing. Core Endian provides built-in “flippers” for most places that need them (e.g., Apple Events).

By: Otto

Otto — Wed, 16 Feb 2011 20:53:48 +0000

Even if someone doesn’t program in C++, if they are hardcore about their craft I still recommend reading Effective C++. There’s a lot of stuff there that will make them a better Objective-C programmer.

Question: Are there endian issues with the ‘abcd’ literal? Does it compile to a different sequence of bytes on PPC vs Intel?

By: Peter Hosey

Peter Hosey — Sun, 11 Jul 2010 05:47:50 +0000

Guh. This reading, Cédric, I understood what you were saying just fine: While you’re using Xcode 3.1, you may accumulate undeclared selectors that it won’t warn about, which will break your build when you finally do upgrade your Xcode. Sorry about that.

By: Peter Hosey

Peter Hosey — Thu, 06 May 2010 07:05:38 +0000

Cédric Luthi: It’ll break the build in Xcode 3.1, too. “Treat Warnings as Errors” isn’t new in 3.2; it’s existed for a long, long time. It just worked differently before (it’d add a warning saying “warnings treated as errors”, then display the warnings as warnings but fail the build anyway; now it displays both warnings and errors as errors).

And I don’t see what any specific warning has to do with that.

By: Cédric Luthi

Cédric Luthi — Thu, 06 May 2010 06:38:30 +0000

Actually, setting GCC_WARN_UNDECLARED_SELECTOR in Xcode 3.1 may hurt if you also define Treat Warnings as Errors and if someone else uses the same project with Xcode 3.2. Warnings will go unnoticed with Xcode 3.1 and will break the build with Xcode 3.2.

By: Sean M

Sean M — Wed, 03 Mar 2010 22:29:27 +0000

I once spent quite some time trying to enable as many warnings as possible by scouring the gcc man page. Below is my .xcconfig file that contains various warning flags. When Xcode has a specific option for a warning, I use it, if it doesn't exist I use the gcc flag. Note that some warnings do/don't work with some compilers. Our large Obj-C/Obj-C++ app builds warning-free with these settings. (RR is our company prefix, BW stands for Build Warning). This assumes gcc 4.2 and Xcode 3.2. Hope it's helpful.

// C only warnings.
GCC_WARN_ABOUT_MISSING_PROTOTYPES = YES
RR_BW_C_NOTCLANG = -Wdiv-by-zero
RR_BW_C = -Wstrict-prototypes -Wold-style-definition -Wnested-externs -Wmissing-prototypes -Wmissing-declarations $(RR_BW_C_NOTCLANG)
OTHER_CFLAGS = $(RR_BW_C)

// C++ only warnings.
GCC_WARN_HIDDEN_VIRTUAL_FUNCTIONS = YES
GCC_WARN_ABOUT_INVALID_OFFSETOF_MACRO = YES
GCC_WARN_NON_VIRTUAL_DESTRUCTOR = YES
RR_BW_CPP = -Wabi -Wctor-dtor-privacy -Wsign-promo -Woverloaded-virtual
OTHER_CPLUSPLUSFLAGS = $(RR_BW_CPP)

// Objective C only.
GCC_WARN_STRICT_SELECTOR_MATCH = YES
GCC_WARN_UNDECLARED_SELECTOR = YES
RR_BW_OBJC = 

// For all C-based languages.
GCC_WARN_FOUR_CHARACTER_CONSTANTS = YES
GCC_WARN_ABOUT_MISSING_NEWLINE = YES
GCC_WARN_ABOUT_DEPRECATED_FUNCTIONS = YES
GCC_WARN_SHADOW = YES
GCC_WARN_CHECK_SWITCH_STATEMENTS = YES
GCC_WARN_INITIALIZER_NOT_FULLY_BRACKETED = YES
GCC_WARN_MISSING_PARENTHESES = YES
GCC_WARN_SIGN_COMPARE = YES
GCC_WARN_TYPECHECK_CALLS_TO_PRINTF = YES
GCC_WARN_ABOUT_RETURN_TYPE = YES
GCC_WARN_64_TO_32_BIT_CONVERSION = YES

// Managed Object Model compiler.
MOMC_NO_INVERSE_RELATIONSHIP_WARNINGS = YES

// Note that it is important to start with -Wall and -Wextra because if they were at the end, they may reset some other options.
RR_BW_ALL_NOTCLANG = -Wlarger-than-30000 -Winvalid-pch
RR_BW_ALL_NOTGCC40 = -Wstrict-overflow=2 -Wvolatile-register-var -fdiagnostics-show-option
RR_BW_ALL = -Wall -Wextra -Wundef -Wendif-labels -Wpointer-arith -Wcast-align -Wwrite-strings -Wformat=2 -Wno-format-nonliteral -Wmissing-format-attribute -Wpacked -Wredundant-decls -Wdisabled-optimization -Wno-strict-aliasing -Wfloat-equal -Winit-self -Wextra-tokens -Wmissing-field-initializers $(RR_BW_ALL_NOTGCC40) $(RR_BW_ALL_NOTCLANG)

// Warnings to enable occasionally.  They give some good warnings, but not always.
//GCC_WARN_EFFECTIVE_CPLUSPLUS_VIOLATIONS = YES
//RR_BW_ALL_OCCASIONAL = -Wcast-qual -Wunsafe-loop-optimizations -funsafe-loop-optimizations -Wswitch-enum -Wstack-protector -Wformat-nonliteral

// Combine.
WARNING_CFLAGS = $(RR_BW_ALL) $(RR_BW_OBJC)

// TODO: would like to use:
//  GCC_WARN_PEDANTIC = YES • too annoying with Obj-C
//  -Wcast-qual • gives false positives with Obj-C 4625600. But turn on periodically, as it finds real problems!
//  -Wstrict-aliasing • is unnecessarily annoying 5509903 5509977
//  -Wstrict-aliasing=2 would be even nicer, though it is documented to give false positives
//  -Wformat-nonliteral (part of -Wformat=2) • causes problems with NSLocalizedStringFromTable 6835692

By: Jonathan Mitchell

Jonathan Mitchell — Wed, 09 Dec 2009 14:47:13 +0000

Personally I like the unused parameter warning.

Yes, it creates, a log of pragma clutter, especially for callbacks, but when reviewing code I find that those pesky pragmas do provide a bit of instant feedback that would otherwise escape me.

The Apple docs on warnings are helpful too.
http://developer.apple.com/tools/xcode/compilercodewarnings.html

Good post.

By: Uli Kusterer

Uli Kusterer — Tue, 01 Dec 2009 09:19:52 +0000

The Four-Character Literals warning isn’t completely pointless. Since they’re essentially an Apple addition to C, you want that warning turned on in cross-platform code. So, I wouldn’t say “for no benefit”, I’d say “I’m writing Mac-only code, so don’t need it.”

By: Ahruman

Ahruman — Sat, 28 Nov 2009 17:18:04 +0000

I habitually set “-Wall -Wextra -Wno-unused-parameter” in Other Warning Flags, and turn on Treat Warnings as Errors (or -Werror if you like to copy and paste). The only downside is I sometimes need to deal with other people’s code. :-)

By: Uli Kusterer

Uli Kusterer — Mon, 09 Nov 2009 15:39:14 +0000

Re: Treat Warnings as Errors:

If you can use that, do it. But I can’t use that in most of my shipping projects, because they need to build and run on several platforms (10.4, 10.5, 10.6 ATM), and Apple’s been madly changing their compilers with each version of Xcode, so I get warnings about settings that used to be necessary to build correctly, and are now deprecated, that would stop the build immediately :-(

By: Blake C.

Blake C. — Mon, 09 Nov 2009 04:29:16 +0000

Peter: That’s better than editing all of those settings for each project, but you make a good point. I’d say file a bug :)

By: Christopher Lloyd

Christopher Lloyd — Mon, 09 Nov 2009 02:11:18 +0000

“Multiple Definition Types for Selector” is only relevant for the GNU Objective-C runtime which has the mis-feature of trying to associate types with a selector. Largely pointless these days, should probably be deprecated all together.