1# @(#)structures 5.4 (Berkeley) 10/4/95 2 3There are three major data structures in this package, plus a single data 4structure per screen type. The first is a single global structure (GS) 5which contains information common to all files and screens. It hold 6global things like the input key queues, and functions as a single place 7to hang things. For example, interrupt routines have to be able to find 8screen structures, and they can only do this if they have a starting 9point. The number of globals in nvi is dependent on the screen type, but 10every screen type will have at least one global, __global_list, which 11references the GS structure. 12 13The GS structure contains linked lists of screen (SCR) structures. 14Each SCR structure normally references a file (EXF) structure. 15 16The GS structure has a set of functions which update the screen and/or 17return information about the screen from the underlying screen package. 18The GS structure never goes away. The SCR structure persists over 19instances of screens, and the EXF structure persists over references to 20files. 21 22File names have different properties than files themselves, so the name 23information for a file is held in an FREF structure which is chained from 24the SCR structure. 25 26In general, functions are always passed an SCR structure, which usually 27references an underlying EXF structure. The SCR structure is necessary 28for any routine that wishes to talk to the screen, the EXF structure is 29necessary for any routine that wants to modify the file. The relationship 30between an SCR structure and its underlying EXF structure is not fixed, 31and various ex commands will substitute a new EXF in place of the current 32one, and there's no way to detect this. 33 34The naming of the structures is consistent across the program. (Macros 35even depend on it, so don't try and change it!) The global structure is 36"gp", the screen structure is "sp", and the file structure is "ep". 37 38A few other data structures: 39 40TEXT In nvi/cut.h. This structure describes a portion of a line, 41 and is used by the input routines and as the "line" part of a 42 cut buffer. 43 44CB In nvi/cut.h. A cut buffer. A cut buffer is a place to 45 hang a list of TEXT structures. 46 47CL The curses screen private data structure. Everything to 48 do standalone curses screens. 49 50MARK In nvi/mark.h. A cursor position, consisting of a line number 51 and a column number. 52 53MSG In nvi/msg.h. A chain of messages for the user. 54 55SEQ In nvi/seq.h. An abbreviation or a map entry. 56 57TK The Tcl/Tk screen private data structure. Everything to 58 do standalone Tcl/Tk screens. 59 60EXCMD In nvi/ex/ex.h. The structure that gets passed around to the 61 functions that implement the ex commands. (The main ex command 62 loop (see nvi/ex/ex.c) builds this up and then passes it to the 63 ex functions.) 64 65VICMD In nvi/vi/vi.h. The structure that gets passed around to the 66 functions that implement the vi commands. (The main vi command 67 loop (see nvi/vi/vi.c) builds this up and then passes it to the 68 vi functions.) 69