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How to make sure sscanf reads to the end of the line

I needed to do this for GNOME bug 453678, and it wasn’t very obvious. In the end I thought of a way, and I’ve tested it with gcc on GNU/Linux and HP C on OpenVMS to make sure it wasn’t just a GNU thing. (No, this doesn’t imply that I’m introducing a policy of building Metacity on OpenVMS in future.)

GEIN $ type test.c
#include <stdio.h>
#include <string.h>

void
check(char *string)
{
  int workspace = -1;
  int chars = 0;

  sscanf (string, "Workspace %d%n", &workspace, &chars);

  printf ("Input is [%s], workspace number is %d, fully=%s\n",
      string, workspace, *(string+chars)=='\0'?"Yes":"No");
}

int
main(int argc, char**argv)
{
  check ("Workspace 1 is very nice");
  check ("Workspace 2");
  check ("I like beer");
}

GEIN $ cc test
GEIN $ link test
GEIN $ run test
Input is [Workspace 1 is very nice], workspace number is 1, fully=No
Input is [Workspace 2], workspace number is 2, fully=Yes
Input is [I like beer], workspace number is -1, fully=No
GEIN $

OpenVMS testing courtesy of gein.vistech.net .

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This entry was posted on Friday, March 21st, 2008 at 1:30 am and is filed under planet. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

3 Responses to “How to make sure sscanf reads to the end of the line”

  1. Stef says:
    March 21, 2008 at 9:32 am

    You could also use the fact that sscanf returns the number of fields successfully read. Put a dummy %c at the end of the format and check that
    the result is equal to the number of % fields before it:

    void
    check(char *string)
    {
    char dummy;
    int workspace ;

    int NB_FIELD=1 ;
    int nb = sscanf (string, “Workspace %d%c”, &workspace, &dummy);

    printf (“Input is [%s], fully=%s\n”,
    string, (nb==NB_FIELD) ? “Yes”:”No”);
    }

  2. Benoît Dejean says:
    March 21, 2008 at 10:41 am

    Or you could just check sscanf return value ?

  3. Thomas Thurman says:
    March 21, 2008 at 11:39 am

    Ah, I did spend a bit of time thinking about using the return value, but I hadn’t thought of the idea of using the dummy variable. Seems kind of obvious now you point it out :) Thanks.