# GB_SUBST_CALLBACK

    typedef void (* GB_SUBST_CALLBACK ) ( int _index_ , char ** _str_ , long * _len_ );

This is the the type definition of the callback used by the GB.SubstString function.

The callback will receive the following parameters :

- index is the index of the value to substitute.
- str must receive the string to substitute.
- len must receive the length of this string.

You can use the GB.SubstAdd function instead returning the string to substitute with the str and len parameters.