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;* ReadFile - Read from open file to specified buffer. See the CopyFile
;* procedure for another example of using DOS Function 3Fh to read files.
;*
;* Shows:   DOS Function - 3Fh (Read File or Device)
;*
;* Params:  handle - File handle
;*          len - Number of bytes to read
;*          pbuff - Pointer to buffer
;*
;* Return:  Short integer with number of bytes read, or 0 if read error
 
ReadFile PROC \
        USES ds di, \
        handle:WORD, len:WORD, pbuff:PTR BYTE
 
        LoadPtr ds, dx, pbuff           ; Point DS:DX to buffer
        mov     di, dx                  ; Keep string offset in DI
        mov     bx, handle              ; BX = handle
        mov     cx, len                 ; CX = number of bytes to read
        mov     ah, 3Fh                 ; Request DOS read
        int     21h                     ; Read File or Device
        jnc     exit                    ; If ok, exit with bytes read
        sub     ax, ax                  ; Else set error code
exit:   ret
 
ReadFile ENDP
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