You can give a name to the type of an expression using a typedef
declaration with an initializer. Here is how to define name as a
type name for the type of exp:
typedef name = exp;
This is useful in conjunction with the statements-within-expressions feature. Here is how the two together can be used to define a safe ``maximum'' macro that operates on any arithmetic type:
#define max(a,b) \ ({typedef _ta = (a), _tb = (b); \ _ta _a = (a); _tb _b = (b); \ _a > _b ? _a : _b; })
The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within the
expressions that are substituted for a
and b
. Eventually we
hope to design a new form of declaration syntax that allows you to declare
variables whose scopes start only after their initializers; this will be a
more reliable way to prevent such conflicts.