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--- c-brainteasers [2012/11/30 07:58]
joshuawise
+++ c-brainteasers [2013/10/11 00:19]
joshuawise
@@ Line 38: / Line 38: @@
   * //(taken from elsewhere on the Web)// Without running it, what is the output of the following program? \\ ''int main(void) {int n = sizeof(0)["abcdefghij"]; printf("%d\n", n); return 0; }''
     * It is not machine-specific.
+  * A common idiom in C is ''assert(!"That's not gone well")''.  Unfortunately, a common idiom in C amongst careless programmers is ''assert("That's not gone well")'', or the potentially even more amusing ''assert("!That's not gone well")''.  Can you write a macro that chokes with a compile time failure on the latter two cases?
+    * More concretely: it is easy to write a static assert macro that fails to compile if a given expression is either a) false, or b) not compile-time constant.  Your task is to write a static assert macro that fails to compile if a given expression is a) true **and** b) a compile-time constant!
+    * Here are some test cases, if you care: <code>
+ASSERT_CHECKER(time());
+ASSERT_CHECKER(0);
+ASSERT_CHECKER("abc"[2]);
+ASSERT_CHECKER(!"biteme");
+ASSERT_CHECKER("biteme");
+ASSERT_CHECKER(2 + 2);</code> The last two should fail, by the C99 specification.  There is an easier way to do it with a GCC extension, but you do not need any GCC extensions to do this.
+  * //(C++1x-only)// Find a use for the token sequence ''......''.
 I've enabled comments below, but please don't post spoilers.
 ~~DISQUS~~

A small list of C brainteasers

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