Document: WG14/N1360

Date: 2009/02/27

References: WG14/N1321, WG14/N1336, WG14/N1346

Authors: Jim Thomas

Reply to: Jim Thomas <[email protected]>

Subject: benign typedef redefinition

C++ allows a typedef redefinition with the same name as a previous typedef to appear in the same scope, as long as it names the same type. Some C compilers allow similar typedef redefinition as an extension, though C99 does not allow it. Adding benign typedef redefinition to C1x would enhance consistency with C++, standardize some existing practice, and safely eliminate a constraint that is unhelpful and an occasional nuisance to users.

Recommended change (to C1x draft N1336): Change 6.7 #3 from:

If an identifier has no linkage, there shall be no more than one declaration of the identifier (in a declarator or type specifier) with the same scope and in the same name space, except for tags as specified in 6.7.2.3.

to:

If an identifier has no linkage, there shall be no more than one declaration of the identifier (in a declarator or type specifier) with the same scope and in the same name space, except a typedef specifier can be used to redefine the name of any type declared in that scope to refer to the type to which it already refers, and except for tags as specified in 6.7.2.3.