Why can I access to an alement of an array that is not declered? (c)

Question

If I declare an array or table:

int data[5];
data[12]= 23;
printf("%d",data[12]);

Why the program doesn´t give me a warning or an error and outputs the number 23 if that position of the table or array doesn´t exist

That's how C works. You have the power! (to shoot yourself in the foot) — ichramm, Nov 30 '21 at 13:40
Does this answer your question? [Accessing an array out of bounds gives no error, why?](https://stackoverflow.com/q/1239938/11683) — GSerg, Nov 30 '21 at 13:41
In C, you can sometimes get away with [coloring outside the lines](https://en.wiktionary.org/wiki/color_outside_the_lines) (for a little while). :-) — Steve Summit, Nov 30 '21 at 13:49

score 0 · Answer 1 · 2021-11-30T13:52:55.070

In high-level languages, there are functions that prevent you from accessing outside the bounds of an array, by generating an exception (for example, ArrayIndexOutOfBoundsException in Java).

In C, however, arrays are pretty primitive - they are just a sequence of elements with contiguous addresses. There are no bounds checking because it is simply exposing raw memory.

Accessing an invalid index of an array results in Undefined behavior (which essentially means that C simply says what should happen if you access the elements within the bounds of an array. It is left undefined what happens if you try accessing out of bounds. It might work today but it is not legal C, and there is no guarantee that it'll still work the next time you run the program).

It is therefore your responsibility as a developer not to shoot yourself in the foot.

Why can I access to an alement of an array that is not declered? (c)

1 Answers1