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(gcc-300.info)Naming Types

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Naming an Expression's Type
===========================

   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.