Why is type punning bad?

A form of pointer aliasing where two pointers and refer to the same location in memory but represent that location as different types. The compiler will treat both “puns” as unrelated pointers. Type punning has the potential to cause dependency problems for any data accessed through both pointers.

Is type punning undefined behaviour?

The basic rule still applies, however: anything which the standard doesn’t define is undefined behavior. And this clearly falls into this category. I think (but cannot prove) that the intent is that all type-punning be undefined behavior, to be defined by the implementation.

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).

Why is aliasing strict?

“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 Type punning in C++?

Type punning is the possibility of a programming language intentionally subvert the type system to treat a type as a different type. One typical way to do type punning in C++ is to read the member of a union with a different type from the one with which it was written.

What is C++ aliasing?

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.

What are unions CPP?

Purpose of Unions in C/ C++ Union is a user-defined datatype. All the members of union share same memory location. Size of union is decided by the size of largest member of union. If you want to use same memory location for two or more members, union is the best for that. Unions are similar to structures.

Should I use union C++?

Unions are moderately useful in C and largely useless in C++. It would be correct to say that in C++ they’re a “remnant from C++ being based on C”, but not to say they’re “a remnant from the C only days” as if C++ supercedes C.

What is trap representation in C?

A trap representation is a catch-all term used by C99 (IIRC not by C89) to describe bit patterns that fit into the space occupied by a type, but trigger undefined behavior if used as a value of that type.

What is aliasing in list?

Giving a new name to an existing list is called ‘aliasing’. The new name is called ‘alias name’.

Does Java have aliasing?

In Java, Alias is used when reference, which is of more than one, is linked to the same object. The issue with aliasing is when a user writes to a particular object, and the owner for the several other references do not expect that object to change.

What is Type punning C++?

What is union data type?

A union is a special data type available in C that allows to store different data types in the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multiple-purpose.

Why unions are used in C?

Is union same as struct?

A union is like a struct in that it generally has several fields, all of which are public by default. Unlike a struct, however, only one of the fields is used at any given time. In other words, it is a structure that allows the same storage space to be used to store values of different data types at different times.