I have kind of a concept question...
there is a bug in the preceding code but I don't totally understand it. Could somebody explain what is going wrong?? Thanks!Code:struct node { int count; struct node *next; }; int main() { int data = 0; struct node *getdata; getdata->count = data + 1; printf("%d", getdata->count); }
This doesn't point to writable memory.So if you try to write there, you're hosed.Code:struct node *getdata;
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
Can you elaborate? Cause I really want to understand what's going wrong and I still don't really. What would I have to change to make this code work?
A pointer points. Where is your finger pointing at the moment? Nowhere? Same place your pointer is pointing: nowhere.
You need to point to some writable memory before you can write to where it is pointing. Here you are writing to a dangling pointer.
Since this appears to be a linked list type of question that you seem to be withholding, I'd say you need to look into dynamic allocation; since this is the C board, that means malloc/free.Code:struct node *getdata; getdata->count = data + 1;
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
Or if you didn't want to use dynamic memory allocation:
This code would simply print a '0' to the standard input, since data is incremented after it is assigned to count. Using ++data would increment data first, then assign it to count.Code:int main(void) { int data = 0; struct node d; d.count = data++; //assigns data to d.count, then increments data by 1 printf( "%d", d.count ); }
But as Dave has said, look into memory allocation and how variables and initialized. Its always best to start with the basics.
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I think the problem was around dynamic memory allocation, not pre- vs. postfix increment operators, especially since the original program didn't have a ++ in it.
Try googling for "c programming tutorial dynamic memory allocation" or something; I'm sure you'll turn up a page or two. You could also throw in "malloc".
This tutorial might have some relevant information, but it's about pointers and doesn't have anything about memory allocation: http://www.cprogramming.com/tutorial/c/lesson6.html
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