Differences

This shows you the differences between two versions of the page.

--- gcc_extensions [2019/07/25 12:16] – created rpjday
+++ gcc_extensions [2019/07/25 12:53] (current) – [Case ranges] rpjday
@@ Line 6: / Line 6: @@
 ==== Statements and declarations in expressions ====
+A compound statement enclosed in parentheses may appear as an expression in GNU C. This allows you to use loops, switches, and local variables within an expression.
 <code>
@@ Line 11: / Line 13: @@
   ({int _a = (a), _b = (b); _a > _b ? _a : _b; })
 </code>
+==== Local labels ====
+GCC allows you to declare local labels in any nested block scope. A local label is just like an ordinary label, but you can only reference it (with a goto statement, or by taking its address) within the block in which it is declared.
+<code>
+__label__ label;
+</code>
+==== Labels as values ====
+You can get the address of a label defined in the current function (or a containing function) with the unary operator ‘&&’. The value has type void *. This value is a constant and can be used wherever a constant of that type is valid.
+<code>
+void *ptr;
+/* … */
+ptr = &&foo;
+...
+goto *ptr;
+</code>
+==== Nested functions ====
+<code>
+foo (double a, double b)
+{
+  double square (double z) { return z * z; }
+  return square (a) + square (b);
+}
+</code>
+See "trampolines."
+==== Nonlocal gotos ====
+Use ''%%__builtin_setjmp%%'' and ''%%__builtin_longjmp%%''.
+==== Constructing function calls ====
+==== typeof ====
+<code>
+#define max(a,b) \
+  ({ typeof (a) _a = (a); \
+      typeof (b) _b = (b); \
+    _a > _b ? _a : _b; })
+</code>
+==== Conditionals ====
+Equivalent:
+<code>
+x ? x : y
+x ? : y
+</code>
+==== Non-constant initializers ====
+==== Designated initializers ====
+==== Case ranges ====
+<code>
+case low ... high:
+</code>
+Don't forget spaces.