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 spawnve()               Execute Program Using Arg Array, Environment

 #include   <process.h>

 int        spawnve(modeflag,pathname,argv,envp);
 int        modeflag;                    Execution mode for parent process
 char       *pathname;                   Path name of file to be executed
 char       *argv[];                     Array of pointers to arguments
 char       *envp[];                     Array of pointers to environment

    spawnve() loads and executes a new child process.  'modeflag'
    determines whether the parent process is overlaid in memory or waits
    for the new process to be completed.  'modeflag' should be set to one
    of the following values (defined in <process.h>):

         P_WAIT     Wait for child process to finish.

      P_OVERLAY     Child process overlays the area in memory occupied by
                    parent process.  This is equivalent to using the
                    execv() function.

       P_NOWAIT     executes the parent process concurrently with the
                    child. This, however, is not currently implemented
                    and returns an error value.

    'pathname' specifies the path and file name of the child process.  If
    'pathname' includes a file name extension, only that file is searched
    for. If 'pathname' ends with a period (.), then 'pathname' without an
    extension is searched for.  If 'pathname' has no extension and does
    not end with a period, then spawnve() searches for 'pathname'; if
    'pathname' is not found, the extension .COM is appended and the
    search is repeated. If that is not found, .EXE is appended and the
    search is repeated.

    'argv' points to an array of pointers; the pointers, in turn, point
    to the strings that are passed to the child process as command-line
    parameters.  The 'argv' array is terminated by a NULL pointer at
    'argv[n+1]'. 'argv[0]' must not be NULL; it is usually set to
    'pathname'.

    The combined length of all the strings forming the argument list
    passed to the child process must not exceed 128 bytes.  This includes
    "n" (for 0-n arguments) and space characters (required to separate
    the arguments), but does not include the null ('\0') terminating
    character.

    'envp' points to an array of pointers that, in turn, point to strings
    that define environment variables.  These strings usually have the
    form ENVVAR=value; "ENVVAR" is the name of the variable and "value'
    is the string value to which it is set.  The 'envp' array is
    terminated by a NULL pointer.  If 'envp' is NULL, the child process
    acquires the environment of the calling process.

       Returns:     All spawn functions return the exit status of the
                    child process.  The exit status is 0 if the process
                    terminated normally. The child process can set the
                    exit status to a nonzero value by calling exit() with
                    the desired return value.

                    If not set by the child process, a positive exit
                    status indicates an error by an abort() or an
                    interrupt.

                    A return value of -1 indicates an error, and 'errno'
                    is set to one of the following:

                    E2BIG       Argument list or environment list too big
                                  (List > 128 bytes, or environment > 32k)
                    EINVAL      Invalid 'modeflag' argument
                    ENOENT      File or path not found
                    ENOEXEC     File not executable
                    ENOMEM      Not enough memory

                    A child process spawned with 'modeflag' set to
                    P_OVERLAY does not return to the calling process.

         Notes:     Any file that is open when a spawn call is made
                    remains open in the child process.  This includes
                    'stdin','stdout', 'stderr', 'stdaux', and 'stdprn'.

                    spawnve() does not preserve the translation modes of
                    open files.  Use setmode() in the child process to
                    set the desired translation modes.

                    Signal settings (see ssignal()) are not preserved.
                    They are reset to the default in the child process.


   Portability:     MS-DOS only.

   -------------------------------- Example ---------------------------------

    The following statements transfer execution to the child process
    "child.exe" and pass it the three arguments "child", "arg1", and
    "arg2".  The PATH environment variable is set to "C:\TEST" for the
    child process.  The exit status of the child is printed upon return.

           #include <process.h>    /* for 'spawnve' and 'P_WAIT' */
           #include <stdio.h>      /* for 'printf' and 'NULL' */
           #include <errno.h>      /* for 'errno', 'ENOENT' and 'ENOMEM' */

           char *args[] = {"child", "arg1", "arg2", NULL};
           char *env[] = {"PATH=C:\\TEST", NULL};

           main()
           {
               int result;

               result = spawnve(P_WAIT, "child.exe", args, env);
               if (result != -1)
                   printf("exit status of child.exe = %d\n", result);
               else {
                   if (errno == ENOENT)
                       printf("child.exe not found in current directory\n");
                   else if (errno == ENOMEM)
                       printf("not enough memory to execute child.exe\n");
                   else
                       printf("error #%d trying to spawn child.exe\n",
                               errno);
               }
           }