Most useful GCC extensions to C language; avoid by using -pedantic
.
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.
#define maxint(a,b) \ ({int _a = (a), _b = (b); _a > _b ? _a : _b; })
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.
__label__ label;
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.
void *ptr; /* … */ ptr = &&foo; ... goto *ptr;
foo (double a, double b) { double square (double z) { return z * z; } return square (a) + square (b); }
See “trampolines.”
Use __builtin_setjmp
and __builtin_longjmp
.
#define max(a,b) \ ({ typeof (a) _a = (a); \ typeof (b) _b = (b); \ _a > _b ? _a : _b; })
Equivalent:
x ? x : y x ? : y
case low ... high:
Don't forget spaces.