0668			[U] '%s' is declared as a typedef and may not be redeclared as a member of a 'struct' or 'union' without an explicit type specifier.
	Explicitly undefined				REFERENCE - ISO:C90-6.5.6 Type Definitions - Semantics

/*PRQA S 781,783,2017,3205,3408,3602 ++*/

typedef int X;

extern void foo(void)
{
    const int X = 0;         /* Message 3334 */
    struct ST
    {
        const X;             /* Message 0668 */
        int   y;
    };
}

See also:

• 3334 This declaration of '%s' hides a more global declaration.