Open System Services Programmer's Guide

Example 2 Calling a Guardian Procedure That Returns a Return Value
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cextdecs.h(FILE_GETINFOBYNAME_)> /* Note 1 */
char *filename;
short typeinfo[5];
int main(int argc, char *argv[]) {
short retcode, physreclen; /* Note 2 */
/* Get Guardian filename and pass it to the Guardian procedure. */
if(argc > 1)
filename = argv[1];
else
filename = "$system.system.stdioh";
retcode = FILE_GETINFOBYNAME_(filename, /* Guardian filename */
(short) strlen(filename), /* filename length */
typeinfo, /* return array of file information */
&physreclen, /* returned physical record length */
, /* desired options, if any Note 3 */
, /* tag or timeout value, if any */
);
/* Check for valid filename. */
if (retcode != 0) {
fprintf(stderr, "retcode = %d\n", retcode);
fprintf(stderr, "Non-existent file or filename in bad format\n");
exit(1);
}
/* Print information for a disk file. */
printf("Filename = %s\n", filename);
printf("device type = %d\n", typeinfo[0]);
printf("device subtype = %d\n", typeinfo[1]);
printf("physical record length = %d\n", physreclen);
if(typeinfo[0] == 3) { /* it’s a disk file */
printf("object type = %d\n", typeinfo[2]);
printf("file type = %d\n", typeinfo[3]);
printf("file code = %d\n", typeinfo[4]);
}
return(0);
}
Note 1
The cextdecs.h library header file contains function prototype declarations for Guardian
procedures you can call directly from a C program. It is important to specify which Guardian
procedures the program will call; otherwise, all function prototype declarations in cextdecs.h
are included in your program. In this program, only the function prototype declaration for the
FILE_GETINFOBYNAME_ procedure is included.
To use cextdecs.h with a native program, you must specify the EXTENSIONS pragma,
because the procedure declarations in cextdecs.h use _tal syntax instead of the pragma
function syntax.
Note 2
The integer into which a value is returned, retcode, is declared as a short integer. This is
because the integer data type in Guardian procedures represents a 16-bit word, while the
integer data type in OSS C programs represents a 32-bit word.
Calling Functions and Procedures in OSS Programs 39