Why NSAssert1, etc instead of NSAssert?

Question

I thought NSAssert couldn't use printf specifiers, but this:

NSAssert(0, @"%@%@", @"foo", @"bar");

works just as you'd expect:

*** Assertion failure in -[MyClass myMethod], <Path>/MyClass.m:84
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException',
    reason: 'foobar'

So what's the point of using NSAssert1, NSAssert2, etc when NSAssert works?

This with Xcode 4.0 and the iOS 4.3 SDK, if that matters. (If it doesn't, I'll update the tags.)

score 18 · Accepted Answer · answered Jun 03 '11 at 07:29

Current versions of NSAssert() use preprocessor variadic macros, i.e., __VA_ARGS__. Since variadic macros are a C99 feature, my guess is that older versions of the SDK didn’t allow variable arguments in NSAssert(), hence the need for NSAssert1(), NSAssert2(), etc.

If you try to compile

NSAssert(0, @"%@%@", @"foo", @"bar");

using -std=c89 or -ansi (ISO C90, an older version of C that doesn’t support variadic macros), you get a compiler error:

error: too many arguments provided to function-like macro invocation
    NSAssert(0, @"%@%@", @"foo", @"bar");

For that code to compile with -std=c89 or -ansi, you need to use NSAssert2():

NSAssert2(0, @"%@%@", @"foo", @"bar");

score 0 · Answer 2 · answered Aug 10 '15 at 07:00

Excellent Answer By Bavarious.

Just adding my single bit to it. For the people who are facing issue Too many arguments provided to function-like macro invocation. Pay attention to the part mentioned as -std=c89 by @Bavarious.

Here is how I got rid of the issue.

Go to build settings -> Apple LLVM 6.1
Find C language dialect
Change to -std=c99

Why NSAssert1, etc instead of NSAssert?

2 Answers2