What is strict aliasing rule?

“Strict aliasing is an assumption, made by the C (or C++) compiler, that dereferencing pointers to objects of different types will never refer to the same memory location (i.e. alias each other.)”

What is the strict aliasing rule and why do we care?

The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior (UB) [CPP-1]. Once we have undefined behavior, all bets are off.

What is aliasing in programming?

In C, C++, and some other programming languages, the term aliasing refers to a situation where two different expressions or symbols refer to the same object. When references access that object in different ways—as both reads and stores—there are consequences for the order in which these mixed accesses can happen.

What is pointer aliasing in C?

Pointer aliasing is a hidden kind of data dependency that can occur in C, C++, or any other language that uses pointers for array addresses in arithmetic operations. Array data identified by pointers in C can overlap, because the C language puts very few restrictions on pointers.

What does it mean to use strict aliasing in C?

“Strict aliasing is an assumption, made by the C (or C++) compiler, that dereferencing pointers to objects of different types will never refer to the same memory location (i.e. alias each other.)”.

Is there such a thing as an aliasing violation?

Secondly, aliasing violations everyone is talking about is about accessing one object as a different object, not about simply having two objects with the same address. As long as there is no type-punning access, there no problem. That was the original idea. Later, type-punning through unions was allowed. – AnT Nov 27 ’17 at 3:01

Why are aliases bad for C and C + +?

As we see here, the aliasing rules give C and C++ compilers leverage that they can use to generate better code. On the other hand, since C is a low-level language and C++ can be used as a low-level language, both permit casting between pointer types, which can end up creating aliases that violate the compiler’s assumptions.

Can you create an alias for a type identifier?

(This mechanism is also referred to informally as a type alias ). You can also use this mechanism to create an alias template, which can be particularly useful for custom allocators. The name of the alias. The type identifier you are creating an alias for.