Reading a variable messes it up?!?!

Posted by EpsilonVector on Stack Overflow See other posts from Stack Overflow or by EpsilonVector
Published on 2010-05-21T12:16:39Z Indexed on 2010/05/21 12:40 UTC
Read the original article Hit count: 175

Filed under:

printf

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threads

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linux

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homework

We have the following line of code:

printf("%d\n", toc->runlist.next);
printf("%d\n", toc->runlist.next);

These are the definitions:

typedef struct thread_overview_control{
    int id[NR_UTHREADS];
    list_t runlist;
    int active_counter;
    int main_thread;
    int need_resched;
} thread_overview_control;

thread_overview_control* toc;

What I'm trying to do is implement user threads. For some reason the output of the above code at the point where our test run crushes is:

12345678  //some address
0         //NOW IT'S NULL?!?!?!

How can this happen?? All we do is read a variable. And the strange thing is, without printf's there are no crashes. What's going on?

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