CODEWITHSUNDEEP
objective-cxcodecompiler-warningsunused-variables
Gregory Higley
Gregory Higley

Reputation: 16558

How can I get rid of an "unused variable" warning in Xcode?

I understand exactly why unused variable warnings occur. I don't want to suppress them in general, because they are incredibly useful in most cases. However, consider the following (contrived) code.

NSError *error = nil;
BOOL saved = [moc save:&error];
NSAssert1(saved, @"Dude!!1! %@!!!", error);

Xcode reports that saved is an unused variable, when of course it isn't. I suspect this is because NSAssert1 is a macro. The NS_BLOCK_ASSERTIONS macro is not defined, so Objective C assertions are definitely enabled.

While it doesn't hurt anything, I find it untidy and annoying, and I want to suppress it, but I'm not sure how to do so. Assigning the variable to itself gets rid of the compiler warning, but I'd rather do it the "right" way if such a thing exists.

Upvotes: 102

Views: 67015

Answers (10)

Trenskow
Trenskow

Reputation: 3793

This is the way you do it in C and therefore also Objective-C.

Even though you do not have warnings enabled, it's always a good idea to mark the return value as explicitly ignored. It also goes to show other developers, that you have not just forgotten about the return value – you have indeed explicitly chosen to ignore it.

(void)[moc save:&error];

EDIT: Compilers ignore casts to void, so it should not affect performance – it's just a nice clean human annotation.

Upvotes: 6

Alex
Alex

Reputation: 9720

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-variable"
    NSUInteger abc; /// Your unused variable
#pragma clang diagnostic pop

SOURCE

Upvotes: 15

0xFADE
0xFADE

Reputation: 832

Make it take up two lines. Separate the declaration and default value

BOOL enabled = NO;

// ...

BOOL enabled;

enabled = NO;

Upvotes: 1

ArNo
ArNo

Reputation: 2648

You can set "No" LLVM compliler 2.0 warning on "Release" enter image description here

Upvotes: 6

João Nunes
João Nunes

Reputation: 3761

try with: __unused attribute. Works in Xcode 5

Upvotes: 9

user3125367
user3125367

Reputation: 3000

The only simple and portable way to mark variable as used is… to use it.

BOOL saved = ...;
(void)saved; // now used

You may be happy with already described compiler-specific extensions, though.

Upvotes: 16

Sherm Pendley
Sherm Pendley

Reputation: 13612

I'm unsure if it's still supported in the new LLVM compiler, but GCC has an "unused" attribute you can use to suppress that warning:

BOOL saved __attribute__((unused)) = [moc save:&error];

Alternatively (in case LLVM doesn't support the above), you could split the variable declaration into a separate line, guaranteeing that the variable would be "used" whether the macro expands or not:

BOOL saved = NO;
saved = [moc save:&error];

Upvotes: 110

Danny Xu
Danny Xu

Reputation: 401

NSError *error = nil;
BOOL saved = [moc save:&error];
NSAssert1(saved, @"Dude!!1! %@!!!", error);
#pragma unused(saved)

Try like this. It is working for me. It will work for you, too.

Upvotes: 22

JOM
JOM

Reputation: 8207

Using Xcode 4.3.2 and found out that this seems to work (less writing)

BOOL saved __unused;

Upvotes: 116

Black Frog
Black Frog

Reputation: 11713

In Xcode you can set the warnings for "Unused Variables." Go to "Build Settings" for the target and filter with the word "unused"

Here is a screenshot: Builld Settings Screenshot

I suggest you only change it for Debug. That way you don't miss anything in your release version.

Upvotes: 38

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