Incorrectly initializing a multi-dimensional array and Memory

Question

While writing some code for an AVR Micro-controller, my code would compile but would crash on run time (When I ran the code on the Micro-controller, the Micro-controller would stop functioning) After doing some troubleshooting, I realized I incorrectly initializing a multi-dimensional array. My question is about how memory for an array is allocated, and is it possible that since there should be data in that memory location and there is not, would this cause the crash?
Suppose I have a 2-dimensional array. Normally, if initialized correctly if could look something like this:

char *monthsDays[12][2] = {
 {"Jan", "31" }, 
 {"Feb", "28" }, 
 {"Mar", "31" }, 
 {"Apr", "30" }, 
 {"May", "31" }, 
 {"Jun", "30" }, 
 {"Jul", "31" }, 
 {"Aug", "31" }, 
 {"Sep", "30" }, 
 {"Oct", "31" }, 
 {"Nov", "30" }, 
 {"Dec", "31" }
};

And say I created it like so:

char *monthsDays[12][2] = {
 {"Jan", "31" }, 
 {"Feb", "28" } 
};

So I have allocated a lot of memory but haven't used it. At run time, is it possible for the unused portion of memory allocated for my array to be used by another part of the program, which in turn cause the crash?

• pm100: no. not without some other bug in your code that we cant see
• bolov: the rest of the array is zero-initialized. So there should be no problems, unless in your specific case you access that area expecting a null-terminating string.
• PhillyNJ: Ok, I'll have to do more troubleshooting. Its hard to re-create outside of the Micro-Controller environment.
• Weather Vane: @bolov it is an array of pointers (to string literals where declared), the undefined ones containing NULL but not zero-terminators
• bolov: @WeatherVane that was my point

Answer 1

When you initialize your array using:

char *monthsDays[12][2] = {
 {"Jan", "31" }, 
 {"Feb", "28" } 
};

monthsDays[2][0] through monthsDays[11][1] are initialized to 0. Dereferencing them will cause UB. Whether the problem is caused by dereferencing these NULL pointers or some other code stepping on these memory, only you can tell that by looking at the rest of your code.