sprintf messing up with my int counter (converting it to an address?)

Question

While playing around with sprintf to figure out how to make it work before adding it to my recover.c code, I ran into a weird (at least for me) situation.

I declare a counter variable (int type), use this variable as an argument for sprintf and, as far as I can tell, successfully create a filename using the output of sprintf. However, when I printf the value of my counter variable (for sanity check), the value of my counter variable has been modified to a super-long number... It is unclear to me WHY sprintf has any effect on the counter and how I can return the counter to be what it used to be (e.g., to add 1 in order to rename the next file appropriately.

My test code is available in this link. Any input will be greatly appreciated!

Answer 1

The problem lies in your declaration of imagenr.

char imagenr = 0;

This creates a variable that holds a single character, not a string. Later, with the sprintf() call, the code copies an 8 char string (7 chars + end of string marker) into that variable, which overwrites adjacent memory. That adjacent memory looks to be the variable n.

You need to declare a character array large enough to handle the content. Remember, once declared a char string var's size can't be changed.

char imagenr[8];
sprintf(imagenr,"%'.3i.jpg", n);

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