In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres.

Conditional execution statements. Iteration statements (loops). Jump statements. Functions. Function declaration. Lambda function declaration. inline specifier. Exception specifications (until C++20). noexcept specifier (C++11). Exceptions. Namespaces. Types. Specifiers. Storage duration specifiers.

Undefined behavior is one of those aspects of the C and C++ language that can be surprising to programmers coming from other languages (other languages try to hide it better).

Advantages of Undefined Behavior C and C++ have undefined behaviors because it allows compilers to avoid lots of checks. Suppose a set of code with greater performing array need not keep...

Undefined behavior is a term used in the C standard. NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or...

Undefined behavior (often abbreviated UB) is the result of executing code whose behavior is not well defined by the C++ language. In this case, the C++ language doesn't have any rules determining what...

#1 undefined behavior: behavior, upon use of a nonportable or erroneous program construct or of erroneous data, for which this International Standard imposes no requirements.

A study of undefined behavior on various platforms, compilers, and tools.

Other undefined behaviors, such as trying to get a value from a pointer that hasn't been assigned One way to spot undefined behavior is comparing the program running when compiled in debug...

In computer programming, undefined behavior is a feature of some programming languages—most famously C.[1] In these languages, to simplify the specification and allow some flexibility in...

"Undefined behavior" means "all bets are off", and you can no longer depend on the code to do what you would normally think it would do... Regards, Ray L. I have removed the warning, by disabling...

Some people think that undefined behavior is caused only by gross errors (accessing outside the bounds of the array, for instance) or inadequate constructions (i = i++ + ++i, for example).

In many languages, when you are unsure of a particular detail of the language, you can often "just run it" and see what happens. This might work in another language...

Undefined behaviour occurs when a program breaks the rules of the language in a way that is not detected until runtime. It affects the entire program.

Undefined behavior — In computer programming, undefined behavior is a feature of some programming languages most famously C.[1] In these languages, to simplify the specification and...

The original purpose of undefined behavior was for implementation flexibility. In other words, it's slack that allows a compiler to produce appropriate and efficient code for its target platform.

40 Comments on Undefined Behavior in 2017. This post is jointly authored by Pascal Cuoq and John Regehr. Recently we've heard a few people imply that problems stemming from undefined behaviors...

If you experience a Heisenbug, think about undefined behavior in your program. Undefined behavior is almost always caused by a defect. In particular, consider the following

Common undefined behaviours in C++ programming. Awkward behaviour of delete operator on arrays in JavaScript. JavaScript undefined Property.

Finding undefined behaviour in C for embedded system. I just started at a small company and there is a hot-needle-built software for micro controllers written in C which we are now starting to clean up to...

Undefined behavior in programming languages can introduce difficult to diagnose bugs and even lead to security vulnerabilities in your App. Learn more about undefined behavior...

Undefined behaviour is happening not because C is violating precedence rule. Precedence (and associativity which is used when precedence of operators are same) rule is used to specify the...

Undefined Behavior occurs when running code whose behavior is not described by the programming language specification. Languages like C and C++ have quite a lot of undefined behavior to allow compilers the opportunity to generate efficient code for different architectures.

Undefined behavior. Although C++ is a low-level language, the abstract machine is surprisingly strict about which pointers may be formed and how they can be used.

The union trick is also not valid, because only one member of a union can be "active". When we set f it becomes active and i is thus inactive. Reading from an inactive member results in undefined behavior.

It contains undefined behavior, which the standard also says makes the program erroneous. Therefore, the standard imposes no requirements on what the behavior should be.