Question

I have strange program behavior while trying to read a value from a structure after assigning a value to it. I’m showing the related structure and function below:

/*Data struct for cor_entry */
struct cor_entry {
    struct cor_entry * pre_entry;
    struct cor_entry * next_entry;
    long long unsigned int entry_data;
};

I’ve commented out most of my function to highlight the problem:

/* update correlation table */
void cor_table_update(long long unsigned int cor_table_data, 
    struct cor_entry **cor_table_head_ptr, 
    struct cor_entry **cor_table_tail_ptr, 
    int *entry_num, 
    const int MAX_NUM)
{
    struct cor_entry *cor_table_entry;
    int cor_hit=0;

    //test code 
    //cor_table_head=cor_table_tail=(struct cor_entry*)calloc(1, sizeof(struct cor_entry));
    //printf("original cor_entry_num=%d\n",*entry_num);

    ////////////////////////code for test///////////////////////////////

    cor_table_entry=(struct cor_entry*)calloc(1, sizeof(struct cor_entry));
    printf("The cor_table_entry=%x\n",cor_table_entry);
    cor_table_entry->entry_data=cor_table_data;
    if (cor_table_entry->entry_data==cor_table_data)
    { 
        printf("The assignment is correct!\n");
        printf("the cor_enrty_data=%x, stored data=%x,\n",
            cor_table_data,
            cor_table_entry->entry_data);
    }

    // ... rest of function
}

And I get this output while running the program:

The cor_table_entry=8c09a58
The assignment is correct!
the cor_enrty_data=8ffc8, stored data=0,
The cor_table_entry=8c09a70
The assignment is correct!
the cor_enrty_data=8ffc8, stored data=0,
The cor_table_entry=8c09a88
The assignment is correct!
the cor_enrty_data=8ffc8, stored data=0,
The cor_table_entry=8c09ae8

Could someone shed some light on this problem? I’m using the GCC-3.4.6 compiler.

Answer 1

Try to compile with -Wall. GCC should then tell you that the sizes of the % format specifiers and the printf() arguments don’t match. Try %llx instead of %x. That should fix the issue.