form_field_userptr.3x man page
set_field_userptr, field_userptr — associate application data with a form field
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 a pointer (which may be NULL). It does not set errno.
The function set_field_userptr returns E_OK (success).
The header file <form.h> automatically includes the header file <curses.h>.
These routines emulate the System V forms library. They were not supported on Version 7 or BSD versions.
The user pointer is a void pointer. We chose not to leave it as a char pointer for SVr4 compatibility.
Juergen Pfeifer. Manual pages and adaptation for new curses by Eric S. Raymond.