Why is Pointer Arithmetic Exceeding Array Bounds Undefined Behavior in C ?

Why is Pointer Arithmetic that Exceeds Array Bounds Undefined Behavior?

When manipulating arrays in C, it's common practice to access elements using pointers. However, there are certain pitfalls when performing pointer arithmetic, especially when exceeding the bounds of an array. Here's why such arithmetic is considered undefined behavior:

Pointers are Not Integers

Contrary to popular expectations, pointers do not behave exactly like integers. Indicators have their own behaviors and are subject to specific rules. When a value is added to a pointer, it does not add that value to the content of the pointer but to the memory address it points to.

Undefined Behavior

The C standard states that arithmetic A pointer outside the bounds of the array is a defined behavior. This simply means that the compiler does not have to specify how he would act in this case, leaving the result open to interpretation.

Exceptions to the Limit

While it is generally forbidden to exceed the limit Matrix When using pointer arithmetic, there is one important exception. According to Article 5.7, paragraph 5 of Standard C 11, an expression that is one degree greater than the limit of the matrix is ​​allowed. However, the result of this expression is indefinite and should not be relied upon.

Hidden Danger

Even if the pointer reference is not removed out of bounds, the calculation procedure is still risky . Overcalculation of indicators can lead to comparing indicators in the wrong way and performing other calculations that can lead to unexpected results and data corruption.

Precautionary Principle

To avoid these risks, It is best to stick to the basic rules and not go beyond the bounds of the matrix when performing index calculation. Instead, use methods such as range checking or using secure indexes to ensure that data is accessed safely.

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