Category : Files from Magazines
Archive   : DDJ0988.ZIP
Filename : MOON.LIS

_ARGUMENTS AND AUTOMATIC VARIABLES IN ASSEMBLY LANGUAGE_
by
Raymond Moon

LISTING ONE

1 page 60,132
2 title FILE_LENGTH - Determine File Length In Bytes
3 name FILE_LEN
4
5 comment @
6 FILE_LENGTH() V 1.00
7 -------------------------------------------------------
8 NAME
9 file_length() Determine file length in bytes
10
11 SYNOPSIS
12 length = file_length(filename, attribute);
13 long length; length of file in bytes
14 char *filename; path\filename.ext
15 unsigned int attribute; file attribute used
16 in search
17
18 DESCRIPTION
19 This function uses DOS function 4eh, Find First
20 File, to return with the filelength. So that this
21 function does not corrupt the current Data Transfer
22 Area, DTA, this function moves the DTA to its own
23 automatic variable area. If the file is not found,
24 -1L is returned.
25
26 This function allows any kind of file to be found by
27 specifying the file attribute. The following #define
28 statements can be used to define the various file
29 attributes:
30
31 #define NORM 0x00 /* Normal file */
32 #define RO 0x01 /* Read-only file */
33 #define HID 0x02 /* Hidden file */
34 #define SYS 0x04 /* System file */
35 #define VOL_ID 0x08 /* Volume ID */
36 #define SUBDIR 0x10 /* Subdirectory */
37 #define ARCH 0x20 /* Archive file */
38
39 The bit or operator, |, can be used to combine
40 several attributes. For example:
41
42 length = file_length("filename.ext", RO|HID|SYS);
43
44 All normal, read-only, hidden, and system files will
45 be searched for a match to "filename.ext."
46
47 This procedure was assembled using MICROSOFT MASM
48 V5.0 with the switches, /v /ml /z, set.
49
50 CAUTION
51 None.
52
53 RETURNS
54 File length as a long. -1L signifies an error.
55
56 AUTHOR
57 Raymond Moon - 18 Nov 87
58
59 Copyright (c) 1987, MoonWare
60 ALL RIGHTS RESERVED
61
62 HISTORY
63 Version - Date Remarks
64 1.00 - 18 Nov 87 - Orginal
65
66 @
67
68 ;----------------------------
69 ; Define the segments for the memory model so that
70 ; they can link with Microsoft C.
71
72 _TEXT segment byte public 'CODE'
73 _TEXT ends
74
75 _DATA segment word public 'DATA'
76 _DATA ends
77
78 CONST segment word public 'CONST'
79 CONST ends
80
81 _BSS segment word public 'BSS'
82 _BSS ends
83
84 DGROUP group _DATA, CONST, _BSS
85
86 ;----------------------------
87 ; Define the assume directive so MASM knows to what
88 ; the segment registers point
89
90 assume cs:_TEXT, ds:DGROUP, ss:DGROUP, es:DGROUP
91
92 ;----------------------------
93 ; Define the structures for passed parameters and
94 ; automatic variables.
95
96 PARMS struc
97 dw 2 dup (?)
98 FILENAME dw ?
99 ATTR dw ?
100 PARMS ends
101
102 ;----------------------------
103 ; _AUTO structure contains the following variables:
104 ; OLD_DTA Saved address of old DTA
105 ; NEW_DTA Start of NEW_DTA, this first field is
106 ; reserved for subseqent Find Next File
107 ; F_ATTR Attribute found
108 ; F_TIME Time file was last written
109 ; F_DATE Date file was last written
110 ; F_LENGTH Double word file length
111 ; F_NAME Found filename.ext
112
113 _AUTO struc
114 OLD_DTA dd ?
115 NEW_DTA db 21 dup (?)
116 F_ATTR db ?
117 F_TIME dw ?
118 F_DATE dw ?
119 F_LENGTH dd ?
120 F_NAME db 13 dup (?)
121 _AUTO ends
122
123 ;----------------------------
124 ; Define structures for addressing trhe offset and
125 ; segment portions of doubleword pointers and the
126 ; least and most significant words of long intergers.
127
128 DOUBLEWORD_PTR struc
129 OFF dw ?
130 SEGMT dw ?
131 DOUBLEWORD_PTR ends
132
133 LONG_INT struc
134 LSW dw ?
135 MSW dw ?
136 LONG_INT ends
137
138 ;----------------------------
139 ; Start the Code Segment.
140
141 _TEXT segment
142
143 _FILE_LENGTH proc near
144
145 public _FILE_LENGTH
146
147 ;----------------------------
148 ; Standard entry logic. Save calling BP. Set up new
149 ; BP. Define automatic variable addressing base,
150 ; AUTO. Save segment registers are saved as DS and
151 ; ES are used.
152
153 push bp
154 mov bp,sp
155 sub sp, size _AUTO
156 AUTO equ [bp - size _AUTO]
157 push ds
158 push es
159
160 ;----------------------------
161 ; Get and save current DTA address in OLD_DTA. Use
162 ; DOS service 2fh. The address is returned in ES:BX.
163
164 mov ah,2fh
165 int 21h
166 mov AUTO.OLD_DTA.OFF,bx
167 mov AUTO.OLD_DTA.SEGMT,es
168
169 ;----------------------------
170 ; Set up NEW_DTA as the current DTA. Use DOS service
171 ; 1ah. DS = SS assumed.
172
173 mov ah,1ah
174 lea dx,AUTO.NEW_DTA
175 int 21h
176
177 ;----------------------------
178 ; Set up for File First Find, Service 4eh.
179 ; CX = Search attribute
180 ; DS:DX => ASCIIZ string, d:path\filename.ext
181
182 mov ah,4eh
183 mov cx,[bp].ATTR
184 mov dx,[bp].FILENAME
185 int 21h
186
187 ;----------------------------
188 ; Check for Carry Flag set as that indicates that the
189 ; file was not found. If so, put -1L in F_LENGH so
190 ; -1L is returned as file length.
191
192 jnc FL1
193 mov ax,-1
194 mov AUTO.F_LENGTH.LSW,ax
195 mov AUTO.F_LENGTH.MSW,ax
196
197 ;----------------------------
198 ; Restore old DTA, service 1ah.
199 ; DS:DX => old DTA.
200
201 FL1: mov ah,1ah
202 mov dx,AUTO.OLD_DTA.OFF
203 mov ds,AUTO.OLD_DTA.SEGMT
204 int 21h
205
206 ;----------------------------
207 ; Set up AX:DX to return file length.
208
209 mov ax,AUTO.F_LENGTH.LSW
210 mov dx,AUTO.F_LENGTH.MSW
211
212 ;----------------------------
213 ; Exit logic. Restore segment registers. Remove any
214 ; automatic variables. Restore calling BP.
215
216 pop es
217 pop ds
218 mov sp,bp
219 pop bp
220 ret
221
222 _FILE_LENGTH endp
223
224 _TEXT ends
225
226 end




Example 1: Definition of strncpy()

char *strncpy(string1, string2, n);
char *string1; pointer to the first string
char *string2; pointer to the second string
unsigned int n; number of characters to be
copied


Example 2: needs caption


PARMS struc ; Passed arg addressing struc
dw 2 dup(?) ; Saved IP and bp registers
string1 dw ? ; Pointer to 1st string
string2 dw ? ; Pointer to 2nd string
N dw ? ; # char to copy
PARMS ends



Example 3: Automatic variable structure


_AUTO struc ; Auto var addressing struc
INT_1 dw ? ; 1st automatic variable
INT_2 dw ? ; 2nd automatic variable
INT_3 dw ? ; 3rd automatic variable
_AUTO ends


Example 4: Standard entry code

push bp ; Save the called bp
mov bp,sp ; Initialize new frame pointer
sub sp,size _AUTO
; Make room for auto vars
AUTO equ [bp - size _AUTO]
; Auto var addressing base

Example 5: #defines for file attributes to be used with file_length()


#define NORM 0x00 /* Normal file */
#define RO 0x01 /* Read-only file */
#define HID 0x02 /* Hidden file */
#define SYS 0x04 /* System file */
#define VOL_ID 0x08 /* Volume ID */
#define SUBDIR 0x10 /* Subdirectory */
#define ARCH 0x20 /* Archive file */




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