DOCUMENT:Q123729 04-FEB-2002 [masm] TITLE :Accessing Command Line Arguments PRODUCT :Microsoft Macro Assembler PROD/VER::5.1,6.0,6.1,6.11 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Macro Assembler (MASM), versions 5.1, 6.0, 6.1, 6.11 ------------------------------------------------------------------------------- SUMMARY ======= In C, you access command line arguments via the argc and argv parameters in your main function. MASM doesn't have a similarly built-in feature in a main function, but there are two ways to get to the command line arguments for your program. MORE INFORMATION ================ Method One ---------- The first way to get the command line arguments for a MASM program is to access the command tail in the Program Segment Prefix (PSP). The command tail is one or more bytes of ASCII text representing a program's command line arguments. When your program starts, the ds and es segment registers initially point to the PSP. The byte value at PSP+80h is the length of the command tail. Therefore, you can access the command tail length through either ds:80h or es:80h. The command tail itself begins at PSP+81h. The command tail is so named because it contains everything that appears in the command line after the command name. The arguments are unformatted; they appear exactly as the user typed them in, including any extra spaces. It is up to you to parse the command string. Typically, if you use COMMAND.COM to load the program, the first character of the command tail is the space that separated the command name from the first argument. If your program was called from another program, the command tail may not contain the leading space. NOTE: 80h-FFh in the PSP is the default Disk Transfer Area (DTA). Therefore, if you use MS-DOS calls that use the DTA, such as file I/O, the command line arguments will be overwritten. To avoid this problem, either extract the command tail before you do anything else in your code or set up a custom DTA. Method Two ---------- The second way to get the command line arguments for a MASM program is to access the command line at the end of the environment block. The environment block contains zero-terminated ASCII strings, each of which represents the name and value of an environment variable. After the last string in the environment block, there are two zero terminators instead of one. These are followed by the full command line, including the command name that was used to start your program. The segment for the environment block can be found at offset 2Ch in the PSP. Therefore, you will need to load this segment value into a segment register, such as es, and access the environment block from there. REFERENCES ========== For more information on the PSP and the command tail, please see the PSP table in the "Microsoft Macro Assembler Reference." Additional query words: kbinf 5.10 6.00 6.10 ====================================================================== Keywords : Technology : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM610 kbMASM611 Version : :5.1,6.0,6.1,6.11 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2002.