Q45904: Using DosExecPgm() After Changing PATH Environment Variable

Article: Q45904
Product(s): See article
Version(s): 5.10
Operating System(s): OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 25-JUL-1989

Question:

I use the C 5.10 run-time putenv() function to change my PATH
environment variable. I then use the OS/2 DosExecPgm() API call to
start an executable that lies on that path. DosExecPgm() fails to
execute the process, giving me a return code indicating that the file
could not be found. I try the run-time spawnlp() function and it works
correctly. What is the problem? How can I get DosExecPgm() to work?

Response:

The C run-time startup code copies the environment table into DGROUP.
The putenv() run-time function modifies this copy of the environment.
Other C run-time functions, including spawnlp(), will use this copy of
the environment. So, when you alter your path variable

   putenv( "PATH=d:\\whack" );

and look at it

    Path = getenv( "PATH" );

you see that Path does indeed point to the new path. However, then
using an OS/2 API call to check the path variable

   DosScanEnv( "PATH", &Path );

reveals that the path is unchanged. This is because the API functions
deal with the original environment table, not the copy in DGROUP.
DosExecPgm() is no exception, meaning that the original PATH
environment variable will be used rather than the altered copy.

In order to perform a DosExecPgm() of a process that is not on the
original search path but is known to be on another search path, you
may wish to use the DosSearchPath() function in conjunction with
DosExecPgm(), in the following manner:

#define INCL_DOS

#include <os2.h>
#include <stdio.h>

void main( void );

void main()
{
    RESULTCODES    ResCodes;
    char           Fail[256];
    USHORT         ret;
    char           Pgm[256];

    DosSearchPath( SEARCH_CUR_DIRECTORY,    // Start with cur dir
                   "d:\\;c:\\;b:\\whack",   // Search this path
                   "off.exe",               // For off.exe
                   Pgm,                     // Put result path here
                   256 );                   // It's 256 bytes long

    printf( "Pgm path: %s\n", Pgm );

    ret = DosExecPgm( Fail,
                      256,
                      0,
                      NULL,
                      0,
                      &ResCodes,
                      Pgm );

    printf( "DosExecPgm says: %u\n", ret );
    printf( "Fail: %s\n", Fail );
}

This program uses DosSearchPath() to generate a full path to
"off.exe". Each directory in the path passed to DosSearchPath() will
be searched. In this case the current directory will be searched
first, because of the SEARCH_CUR_DIRECTORY flag.

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