2.8.22 redefine_extname

#pragma redefine_extname old_extname new_extname

This pragma causes every externally defined occurrence of the name old_extname in the object code to be replaced by new_extname. As a result, the linker only sees the name new_extname at link time. If #pragma redefine_extname is encountered after the first use of old_extname, as a function definition, an initializer, or an expression, the effect is undefined. (This pragma is not supported in– Xs mode.)

When #pragma redefine_extname is available, the compiler provides a definition of the predefined macro __PRAGMA_REDEFINE_EXTNAME, which lets you write portable code that works both with and without #pragma redefine_extname.

The purpose of #pragma redefine_extname is to allow an efficient means of redefining a function interface when the name of the function cannot be changed. For example, when the original function definition must be maintained in a library, for compatibility with existing programs, along with a new definition of the same function for use by new programs. This can be accomplished by adding the new function definition to the library by a new name. Consequently, the header file that declares the function uses #pragma redefine_extname so that all of the uses of the function are linked with the new definition of that function.

#if    defined(__STDC__)

#ifdef __PRAGMA_REDEFINE_EXTNAME
extern int myroutine(const long *, int *);
#pragma redefine_extname myroutine __fixed_myroutine
#else /* __PRAGMA_REDEFINE_EXTNAME */

static int
myroutine(const long * arg1, int * arg2)
{
    extern int __myroutine(const long *, int*);
    return (__myroutine(arg1, arg2));
}
#endif /* __PRAGMA_REDEFINE_EXTNAME */

#else /* __STDC__ */

#ifdef __PRAGMA_REDEFINE_EXTNAME
extern int myroutine();
#pragma redefine_extname myroutine __fixed_myroutine
#else /* __PRAGMA_REDEFINE_EXTNAME */

static int
myroutine(arg1, arg2)
    long *arg1;
    int *arg2;
{
    extern int __fixed_myroutine();
    return (__fixed_myroutine(arg1, arg2));
}
#endif /* __PRAGMA_REDEFINE_EXTNAME */

#endif /* __STDC__ */