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gcc_extensions [2019/07/25 12:20]
rpjday [Statements and declarations in expressions]
gcc_extensions [2019/07/25 12:52]
rpjday [Nonlocal gotos]
Line 21: Line 21:
 __label__ label; __label__ label;
 </​code>​ </​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>​
 +
 +
 +
gcc_extensions.txt · Last modified: 2019/07/25 12:53 by rpjday