form_field_userptr - associate application data with a
int set_field_userptr(FIELD *field, void*userptr);
void *field_userptr(const FIELD *field);
Every form field has a field that can be used to hold
application-specific data (that is, the form-driver code
leaves it alone). These functions get and set that field.
The function field_userptr returns NULL on error. The
function set_field_userptr returns one of the following:
E_OK The routine succeeded.
System error occurred (see errno).
The header file automatically includes the header
These routines emulate the System V forms library. They
were not supported on Version 7 or BSD versions.
The user pointer should be a void pointer. We leave it as
a char pointer for SVr4 compatibility.
Juergen Pfeifer. Manual pages and adaptation for new
curses by Eric S. Raymond.