Simtel MSDOS 1992 June

home *** CD-ROM | disk | FTP | other *** search

/ Simtel MSDOS 1992 June / SIMTEL_0692.cdr / msdos / ddjmag / ddj8809.arc / MOON.LIS < prev next >

Wrap

File List | 1988-08-22 | 8.4 KB | 292 lines

_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 */ -30-