Q42472: BASIC Cannot Get Child Process’ Return Code or "Error Level"

Article: Q42472
Product(s): See article
Version(s): 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890226-3 B_BasicCom | mspl13_basic
Last Modified: 13-DEC-1989

Languages such as C or Microsoft assembly language allow a program to
set a return code as the program terminates. The only Microsoft BASIC
product capable of setting a return code is Microsoft BASIC PDS
Version 7.00. These return codes are referred to as "error levels" in
MS-DOS batch file processing.

However, it is not possible to determine from a BASIC program (even
BASIC PDS 7.00) what return code was set, even if the C or MASM
program is executed (SHELLed) as a child process of the BASIC parent
program.

This information applies to Microsoft QuickBASIC Versions 2.00, 2.01,
3.00, 4.00, 4.00b, and 4.50; to Microsoft BASIC Compiler Versions 6.00
and 6.00b for MS-DOS and MS OS/2; and to Microsoft BASIC PDS Version
7.00 for MS-DOS and MS OS/2.

BASIC executes a child process with the SHELL "commandstring"
statement. When the child process has terminated, the only means to
determine the returned error code would be a CALL to the DOS INTERRUPT
21h, function 4Dh ("Get Return Code"). Calling this function from
BASIC will execute with no adverse effects but will not retrieve the
correct return code.

It is also not possible to return an error code from a BASIC program
to the process that spawned it. For further information on this, query
on the following words:

   ERRORLEVEL and BASIC

The following is a code example:

'*********************** CODE.BAS **************************
' This program demonstrates that BASIC cannot retrieve
' its child process' return code or "error level".
' You must use QB.LIB or QB.QLB for this program.

' Under the QBX.EXE environment of BASIC PDS 7.00
' the libraries above are QBX.LIB and QBX.QLB respectively.
' Additionally the $INCLUDE filename below would be 'QBX.BI'

REM $INCLUDE: 'qb.bi'
DIM inregs AS RegType, outregs AS RegType
CLS
SHELL "errcode.exe"     ' See C routine below.
inregs.ax = &H4D00
CALL INTERRUPT(&H21, inregs, outregs)
' Blank out AH. The code is returned in AL
outregs.ax = outregs.ax AND &HFF
PRINT "The error level returned was "; outregs.ax
END

/***
   Name this C program ERRORCODE.C and ERRORCODE.EXE.
   When this routine is executed as part of a batch file,
   its return code is correctly interpreted when this
   program is SHELLed to by the above BASIC program.
***/

int
main(void)
{
static char prompt[] = {"inside of the c routine\n"};
printf("%s", prompt);
return(5);
}

REM ************************* TEST.BAT *************************
ECHO OFF
REM This batch file demonstrates that the C routine above
REM correctly returns a return code of 5.
ERRCODE.EXE
IF ERRORLEVEL 5 ECHO THE RETURN CODE IS 5

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