Directory Listing Program

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Let’s write a short program that clears the screen, displays the current disk directory, and asks
the user to enter a filename. (You might want to extend this program so it opens and displays the
selected file.)
C++ Stub Module The C++ module contains only a call to asm_main, so we can call it a
stub module:

// main.cpp// stub module: launches assembly language programextern "C" void asm_main(); // asm startup procvoid main(){asm_main();}

ASM Module The assembly language module contains the function prototypes, several strings,
and a fileName variable. It calls the system function twice, passing it “cls” and “dir” commands.

Then printf is called, displaying a prompt for a filename, and scanf is called so the user can input
the name. It does not make any calls to the Irvine32 library, so we can set the .MODEL directive to
the C language convention:

; ASM program launched from C++ (asmMain.asm).586.MODEL flat,C; Standard C library functions:system PROTO, pCommand:PTR BYTEprintf PROTO, pString:PTR BYTE, args:VARARGscanf PROTO, pFormat:PTR BYTE,pBuffer:PTR BYTE, args:VARARGfopen PROTO, mode:PTR BYTE, filename:PTR BYTEfclose PROTO, pFile:DWORDBUFFER_SIZE = 5000.datastr1 BYTE "cls",0str2 BYTE "dir/w",0str3 BYTE "Enter the name of a file:",0str4 BYTE "%s",0str5 BYTE "cannot open file",0dh,0ah,0str6 BYTE "The file has been opened",0dh,0ah,0modeStr BYTE "r",0fileName BYTE 60 DUP(0)pBuf DWORD ?pFile DWORD ?.codeasm_main PROC; clear the screen, display disk directoryINVOKE system,ADDR str1INVOKE system,ADDR str2; ask for a filenameINVOKE printf,ADDR str3INVOKE scanf, ADDR str4, ADDR filename; try to open the fileINVOKE fopen, ADDR fileName, ADDR modeStrmov pFile,eax.IF eax == 0 ; cannot open file?INVOKE printf,ADDR str5jmp quit.ELSEINVOKE printf,ADDR str6.ENDIF; Close the fileINVOKE fclose, pFilequit:ret ; return to C++ mainasm_main ENDPEND

The scanf function requires two arguments: the first is a pointer to a format string (“%s”), and
the second is a pointer to the input string variable (fileName). We will not take the time to
explain standard C functions because there is ample documentation on the Web. An excellent
reference is Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd
Ed., Prentice Hall, 1988.

 

Directory Listing Program