[fis-gtm-core] Returning Strings to GTM via Callback

[Sean W. <se...@se...>]

I am trying my hand at writing a callback function based on Chapter 11
of the manual but am coming up short.  The function generates a seg
fault and I'm not sure why.

(I think I may need to pre-allocate space for the returned string, but
I'm not sure what the best way to do that would be.  I tried declaring a
parameter as an output variable in the callback table, but am unsure of
how to pass that reference to my C program.)

Any help would be greatly appreciated.

Thanks,
Sean



This program uses the same function and exists normally, printing the
appropriate data:

swoods@sachem:~/mumps/src$ cat stat.c
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

/* GTM Operating System Library */

char* fileinfo (char *filename) {
    struct stat sb;
    printf("FN: %s\n", filename);
    if (stat(filename, &sb) == -1) {
        return "1,File not found!";
    }

    return ctime(&sb.st_mtime);

}

void main(int argc, char *argv[]) {
    struct stat sb;

    if (stat(argv[1], &sb) == 1) {
        printf("Not found!\n");
        exit(1);
    }

    printf("%s\n\n", ctime(&sb.st_mtime));

    printf("%s\n", fileinfo(argv[1]));

    return;
}


Please see the console snippet below for an idea of what I'm doing from
a GTM perspective:

swoods@sachem:~/mumps/src$ echo $GTMXC_os
/home/swoods/mumps/src/os.xc

swoods@sachem:~/mumps/src$ cat $GTMXC_os
/home/swoods/mumps/bin/os.so
fileinfo:   xc_char_t*     fileinfo(I:gtm_char_t*)

swoods@sachem:~/mumps/src$ cat os.c
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

/* GTM Operating System Library */

char* fileinfo (char *filename) {
    struct stat sb;
    printf("FN: %s", filename);
    if (stat(filename, &sb) == -1) {
        return "1,File not found!";
    }

    return ctime(&sb.st_mtime);

}
swoods@sachem:~/mumps/src$ ../bin/fe

GTM>w $&os.fileinfo("/tmp/s")
%GTM-F-KILLBYSIGSINFO1, GT.M process 9365 has been killed by a signal 11
at address 0x005E0B33 (vaddr 0x00000001)
%GTM-F-SIGMAPERR, Signal was caused by an address not mapped to an
object
FN:

Just to show you that the file exists and can be stat'd :

swoods@sachem:~/mumps/src$ stat /tmp/s
  File: `/tmp/s'
  Size: 5               Blocks: 8          IO Block: 4096   regular file
Device: 801h/2049d      Inode: 5505048     Links: 1
Access: (0644/-rw-r--r--)  Uid: ( 1000/  swoods)   Gid: ( 1000/  swoods)
Access: 2011-01-23 15:51:56.865610008 -0500
Modify: 2011-01-23 15:51:56.865610008 -0500
Change: 2011-01-23 15:51:56.865610008 -0500
swoods@sachem:~/mumps/src$