Atari ST series Technical Reference Manual page 110

cess receives as its environment string a copy of the environ­
ment string used by the program that called it.
When mode 0 of Pexec() is used, the call loads the new
program, sets up its basepage, passes the arguments and en­
vironment to it, and executes it. This child process, as it's
called, inherits the parent's standard file descriptors (handles
0-5; see Chapter 6 for more information on standard file han­
dles). When the program ends, the call returns an exit code
from the program (if it passes one) in status. A negative
value in status indicates that the program could not be exe­
cuted (because there wasn't enough memory to run it, or
some other reason). Error returns in status are negative long-
words, while return codes passed from the child process are
word length, with Os in the upper 16 bits of the longword.
Modes 3 and 4 split the functions of mode 0. Mode 3 of
Pexec() takes the same parameters as mode 0, but it just
loads the specified file, sets up its basepage, and returns a
pointer to the basepage in status. It does not execute the pro­
cess. To run the program after it has been loaded with mode
3, you may use mode 4 of Pexec(). This mode uses the
pointer to the program's basepage that was returned by
mode 3 as its only parameter. This pointer is passed in com­
mand. The last mode of Pexec(), mode 5, allocates the largest
free block of memory and creates most of a basepage for it.
Some basepage values, such as the size and address of text,
data, and BSS section, obviously can not be filled in.
Program 5-3 shows how to load and execute a separate
program from within the current one. It demonstrates the
basic principal used by command shell-type programs, which
provide an MS-DOS command-line environment for the ST.
Program 5-3. GPEXEC.C
*•*********«******«***************************/
*
*
GPEXEC.C
*
* Demonstrates use of the GEMDOS
* Pexecf) function to run other programs.
*
I include <osbind.h>
char file[81]; / *
char buffer[83]; /* input line buffer
char 'command;
102
CHAPTER 5
/ * For GEMDOS macro definitions
file name buffer */
/ * pointer to command tail string
*/
*/
* /
*/
* /
*/
* /
* /
* /