topic C Question: char messagebuf[8199999] in Operating System - Linux

C Question: char messagebuf[8199999]

tony j. podrasky — Wed, 05 Jun 2013 22:00:44 GMT

Hello Folks;

I know this isn't exactly an admin question - but I know someone can easily answer it.

I wrote a simple "grim reaper" program to go through the /var/log/message file

and remove all the useless (as far as I'm concerned) messages that Fedora 16

generates.

Here's a short chunk of code:

"NOTE: the [char messagebuf] is shown with 2 values: one works, one doesn't . They aren't both in the code at the same time] :-)

--------

    char messagebuf[8199999];    [NOTE THIS WORKS]
    char messagebuf[10199999];    [NOTE THIS CAUSES segmentation faults]

    FILE *messagefp;

    if((messagefp = fopen(MESSAGE, "r")) == NULL)
        {
        printf ("ERROR: could not open file: %s \n", MESSAGE);
        return 0;
        }

    while(fscanf(messagefp, "%c", &messagebuf[dataend]) == 1)
        ++dataend;

    fclose(messagefp);

--------

The problem is when I increase the value of messagebuf past 8MB, I get a segmentation fault (core dumped) When I execute it regardless of the size of the input file.

Question: how can I make char messagebuf[>8MB]?

regards,

tonyp

Re: C Question: char messagebuf[8199999]

Steven Schweda — Wed, 05 Jun 2013 23:03:44 GMT

Re: C Question: char messagebuf[8199999]

tony j. podrasky — Thu, 06 Jun 2013 00:17:54 GMT

Hello Steven;

Thanx for your help, Steven.

I set the "static char messagebuf[10000000] and it compiled and ran fine.

regards,

tonyp

Re: C Question: char messagebuf[8199999]

Dennis Handly — Sat, 08 Jun 2013 08:49:54 GMT

>I increase the value of messagebuf past 8MB, I get a segmentation fault when I execute it regardless of the size of the input file.

Based on Steven's comments about stack size, if the stack grows towards 0, then the first byte you put into the array will be beyond the top of the stack.