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See searches and references containing UNDEFINED BEHAVIOR!UNDEFINED BEHAVIOR
Unpredictable result when running a program
A computer program exhibits undefined behavior (UB) when it contains, or is executing code for which its programming language specification does not mandate
Undefined_behavior
Topics referred to by the same term
Indeterminate form, in calculus Undefined behavior, computer code whose behavior is not specified under certain conditions Undefined value, a condition where
Undefined
Root-finding algorithm
integer by casting then dereferencing the pointer to it can cause undefined behavior in case the sizes of integer and float do not match on the given architecture
Fast_inverse_square_root
Value indicating that a referenced dataset is invalid or doesn't exist
It might do both at different times, or the comparison might be undefined behavior. Also, in languages offering such support, the correct use depends
Null_pointer
Computer science topic
multiplication by four. Shifts can result in implementation-defined behavior or undefined behavior, so care must be taken when using them. The result of shifting
Bitwise_operation
Form of text that defines C code
the function is entered. The following expression, for example, has undefined behavior: printf("%s %s\n", argv[i = 0], argv[++i]); Code is included from
C_syntax
Computer arithmetic error
signed integer overflow causes undefined behavior. Run-time overflow detection implementation UBSan (undefined behavior sanitizer) is available for C compilers
Integer_overflow
Expression which is not assigned an interpretation
In mathematics, the term undefined refers to a value, function, or other expression that cannot be assigned a meaning within a specific formal system
Undefined_(mathematics)
When a system's behavior depends on timing of uncontrollable events
standards specify that a C or C++ program containing a data race has undefined behavior. A race condition can be difficult to reproduce and debug because
Race_condition
Computer fault caused by access to restricted memory
a segmentation fault. This behavior is not guaranteed by the C standard. Dereferencing a null pointer is undefined behavior in C, and a conforming implementation
Segmentation_fault
Concept in computer programming
catastrophic undefined behavior if they share state. This situation can arise in parallel computing, causing race conditions, but undefined behavior can also
Sequence_point
Programming language
Type conversion Undefined behavior Unions Variables Constructs that behave differently in C and C++ Cyber security Undefined behavior GCC — GNU Compiler
Outline of the C programming language
Outline_of_the_C_programming_language
Differing behavior by identically-coded programs when compiled
unspecified, and undefined behavior. The exact definition of unspecified behavior varies. In C++, it is defined as "behavior, for a well-formed program
Unspecified_behavior
Object which stores memory addresses in a computer program
pointer variables can sometimes point to unexpected locations, causing undefined behavior. To combat this, pointers are sometimes initialized with a null pointer
Pointer (computer programming)
Pointer_(computer_programming)
C function to format and output text
between the format specifiers and count and type of values results in undefined behavior, and the program might crash or vulnerabilities may arise. The format
Printf
Operations transforming individual bits of integral data types
value results in undefined behavior. For example, when shifting a 32 bit unsigned integer, a shift amount of 32 or higher would be undefined. Example: If
Bitwise_operations_in_C
C/C++ specifier referring to constant expression
on preprocessor directives, as well as preventing certain cases of undefined behavior. A variable or a variable template may be declared constexpr if it
Constexpr
General-purpose programming language
requirements, this results in undefined behavior. The Rust documentation includes a list of behaviors considered undefined, including accessing dangling
Rust_(programming_language)
C programming language standard draft planned for release in 2029
meeting: N3272 - "strftime broken-down structure usage (Option 1 - "Undefined Behavior)". N3286 - "Floating-point exception for Macro Replacements". N3287
C29_(C_standard_revision)
Class of mathematical expression
expression 0 0 {\displaystyle {\tfrac {0}{0}}} is also left undefined. Calculus studies the behavior of functions in the limit as their input tends to some
Division_by_zero
Of a function, an additional effect besides returning a value
system Monad (functional programming) Sequence point Side-channel attack Undefined behaviour Unspecified behaviour Frame problem Spuler, David A.; Sajeev
Side effect (computer science)
Side_effect_(computer_science)
Statement which ends execution of a function and resumes in the main code
returned when the return statement is omitted, while in JavaScript the value undefined is returned. In Windows PowerShell all evaluated expressions which are
Return_statement
Standard macro in the C programming language
compilers, it has generated some debate regarding whether this is undefined behavior according to the C standard, since it appears to involve a dereference
Offsetof
Section of code in a program that can never be executed
C++, some constructs are specified to have undefined behavior. A compiler is free to implement any behavior or none, and typically an optimizing compiler
Unreachable_code
Unary operators that add or subtract one from their operand, respectively
operations should be performed. Such expressions generally invoke undefined behavior, and should be avoided. In languages with typed pointers like C, the
Increment and decrement operators
Increment_and_decrement_operators
Dynamic memory management in the C programming language
value, without checking if the allocation is successful, invokes undefined behavior. This usually leads to crash (due to the resulting segmentation fault
C_dynamic_memory_allocation
Data type that allows for values that are one of multiple different data types
y to 10, and does not result in undefined behavior. let z = unsafe { x.baz }; // This results in undefined behavior, as the value stored in x is not
Union_type
Program function without side effects
executing f() concurrently do not result in a data race, which has undefined behavior in C and C++. The following C++ functions are impure as they lack
Pure_function
Automated software testing technique
race conditions and deadlocks (ThreadSanitizer), to detect undefined behavior (UndefinedBehaviorSanitizer), to detect memory leaks (LeakSanitizer), or to
Fuzzing
Shading language for WebGPU
the web platform. WGSL was developed to be human-readable, avoid undefined behavior common in legacy shading languages, and align closely with WebGPU's
WebGPU_Shading_Language
Phrase used in computer science
inequality FINO Model collapse No free lunch theorem Standard error Undefined behavior Demming, Anna (June 30, 2019). "Machine learning collaborations accelerate
Garbage_in,_garbage_out
Analysis of computer programs without executing them
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Static_program_analysis
Web page displayed to new users of a network
the network with pages already loaded into its web browser, causing undefined behavior (for example, corrupt messages appear) when such a page tries HTTP
Captive_portal
Software development methodology
strcpy(str, input); // Copy input. // ... } The function will result in undefined behavior when the input is over 1000 characters. Some programmers may not feel
Defensive_programming
C++ optimization rule
which behavior-changing optimizations are permitted. The first is that programs exhibiting undefined behavior are exempt; since the observable behavior is
As-if_rule
General-purpose programming language
been developed to help C programmers find and fix statements with undefined behavior or possibly erroneous expressions, with greater rigor than that provided
C_(programming_language)
Object whose state cannot be modified after it is created
from it cannot change (without breaking the type system, leading to undefined behavior). Any reference of that value must be marked const or immutable. Basically
Immutable_object
Russian proverb
type, but this assumption is verified at runtime in order to avoid undefined behavior. The phrase has been used in relation to India–China border disputes
Trust,_but_verify
2020 edition of the C++ programming language standard
represented using two's complement (signed integer overflow remains undefined behavior) a revised memory model various improvements to structured bindings
C++20
Value for unrepresentable data
value of a numeric data type (often a floating-point number) which is undefined as a number, such as the result of 0 0 {\displaystyle {\frac {0}{0}}}
NaN
Multithreading computing anomaly
element on the stack. In C++, as shown here, accessing freed memory is undefined behavior: this may result in crashes, data corruption or even just silently
ABA_problem
Programming language feature
also be polymorphic) Person* p = nullptr; try { typeid(*p); // Not undefined behavior; throws std::bad_typeid. } catch (const bad_typeid& e) { std::println(stderr
Run-time_type_information
Pointer that does not point to a valid object
NULL char c = *p2; // p2 is still a dangling pointer, so this is undefined behavior. return i + c; } The alternative version can be used even to guarantee
Dangling_pointer
Type qualifier denoting the data as being read-only
that is itself declared const by means of a const cast results in undefined behavior according to the ISO C++ Standard. In the example above, if ptr references
Const_(computer_programming)
C++ programming keywords for dynamic memory allocation
operator, rather than delete. Using the inappropriate form results in undefined behavior. C++ compilers are not required to generate a diagnostic message for
New_and_delete_(C++)
Form of source code, without regard to meaning
translation or execution. In some cases, such programs may exhibit undefined behavior. Even when a program is well-defined within a language, it may still
Syntax (programming languages)
Syntax_(programming_languages)
Revision of the C++ programming language released in 2026
Standard C++. The Standard C++ Foundation. Retrieved 6 September 2025. Undefined Behavior, cppreference.com cppreference.com. "C++ attribute: indeterminate
C++26
Inheritable and overridable function or method for which dynamic dispatch is facilitated
class is called. If that function is a pure virtual function, then undefined behavior occurs. This is true even if the class contains an implementation
Virtual_function
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Hyperproperty
Tool to detect memory-related bugs
sanitizer is a programming tool that detects bugs in the form of undefined or suspicious behavior by a compiler inserting instrumentation code at runtime. Sanitizers
Code_sanitizer
Programming language family
and is defined by ANSI Common Lisp as erroneous (resulting in "undefined" behavior in compiled files, because the file-compiler can coalesce similar
Lisp_(programming_language)
American computer scientist
is a computer scientist specializing in compiler correctness and undefined behavior. As of 2016[update], he is a professor at the University of Utah.
John_Regehr
Technique circumventing programming language data typing
resulting pointer is not correctly aligned for the pointed-to type, the behavior is undefined." Therefore one should be very careful with the use of type punning
Type_punning
Unexpected program exit due to an error
Safe mode Single-event upset Storage violation SIGILL SystemRescue Undefined behavior Types of invalid addresses include: Invalid real address Invalid segment
Crash_(computing)
Language for controlling a computer
translation or execution. In some cases, such programs may exhibit undefined behavior. Even when a program is well-defined within a language, it may still
Programming_language
UAT—User Acceptance Testing UAV—Unmanned aerial vehicle UB—Undefined Behavior UBA—User behavior analytics UCS—Universal Character Set UDDI—Universal Description
List of computing and IT abbreviations
List_of_computing_and_IT_abbreviations
1998 esoteric programming language
implementation does not explicitly consider this case either and incurs in undefined behavior. In 2007, Ørjan Johansen created Malbolge Unshackled, a version of
Malbolge
Data type which allows a program to indirectly access a particular value in memory
instead of a value directly, inappropriate use of pointers can lead to undefined behavior in a program, particularly due to dangling pointers or wild pointers
Reference_(computer_science)
Apple's general-purpose, open-source, compiled programming language
array bounds are always checked. Integer overflows, which result in undefined behavior for signed integers in C, are trapped as a run-time error in Swift
Swift_(programming_language)
Form of inter-process communication in computer systems
system functions (practically the system calls). Otherwise, it is an undefined behavior. It is suggested to simply set some volatile sig_atomic_t variable
Signal_(IPC)
Natural number
32-bit limit—generally if the underlying engine has undefined behavior, instead of a wraparound behavior, for integer overflow. A well-known example in video
2,147,483,647
Binary arithmetic algorithm
signed int type (the default for int). Signed integer overflow is an undefined behavior in C and thus modular arithmetic is not guaranteed by the standard
XOR_swap_algorithm
State of being protected from memory access bugs
negative offset. In C++, because dereferencing a null pointer is undefined behavior, compiler optimizations may cause other checks to be removed, leading
Memory_safety
Form of computer memory allocation
there is no need to explicitly free the memory, there is a risk of undefined behavior due to stack overflow. The function was present on Unix systems as
Stack-based_memory_allocation
Concepts in theoretical computer science
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Safety and liveness properties
Safety_and_liveness_properties
Graph data structure
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
E-graph
Set of rules defining correctly structured programs for the Rust programming language
at compile time, preventing dangling pointers and other forms of undefined behavior. Rust's type system separates shared, immutable references of the
Rust_syntax
operating system and software running within it to crash or exhibit undefined behavior. UMC produced a small quantity of clock doubling processors labeled
UMC_Green_CPU
Rules to verify computer program correctness
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Hoare_logic
Fundamental problem in computer science
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Path_explosion
In computing, an operation whereby a process creates a copy of itself
the exec family (and a select few other operations) gives rise to undefined behavior. As with vfork, the child borrows data structures rather than copying
Fork_(system_call)
Universal subtype in logic and computer science
inhabited, its term(s) typically correspond to error conditions such as undefined behavior, infinite recursion, or unrecoverable errors. In Bounded Quantification
Bottom_type
C standard library for Android operating system
beyond glibc's to catch code that — while not necessarily causing undefined behavior — is obviously incorrect. Because this new implementation requires
Bionic_(software)
Programming language with English-like syntax
not yet completed, the COBOL 2002 standard stipulates that the behavior is undefined. The reason is that COBOL, rather than a "return address", operates
COBOL
Technique for creating lexically scoped first class functions
the scope of a referenced object, invoking its operator() causes undefined behavior since C++ closures do not extend the lifetime of their context. import
Closure (computer programming)
Closure_(computer_programming)
Process of analyzing computer program behavior
In computer science, program analysis is the process of analyzing the behavior of computer programs regarding a property such as correctness, robustness
Program_analysis
Part of a computer program where a given name binding is valid
is known as variable hoisting. Behavior of names in context that have undefined value differs: in Python use of undefined names yields a runtime error,
Scope_(computer_programming)
Computer memory management methodology
segmentation fault (violation of memory protection) and other forms of undefined behavior. Pointers to deleted objects become wild pointers if used post-deletion;
Manual_memory_management
Order of accesses to computer memory by a CPU
would normally be classified as an ill-formed program exhibiting undefined behavior), the adverse results of an aggressive code-optimization transformation
Memory_ordering
Memory-safe dialect of the C programming language
performance reasons they did not. Calling foo(NULL); will result in undefined behavior (typically, although not necessarily, a SIGSEGV signal being sent
Cyclone (programming language)
Cyclone_(programming_language)
Topics referred to by the same term
Soviet World War II machine gun Ubiquitin, a small regulatory protein Undefined behavior, in computer science, operations that are unspecified Universal Beam
UB
Rust software and development tools
Rust's mid-level intermediate representation (MIR), used for checking undefined behavior. Rustfmt — formatting tool for Rust code Sanitizer — Rust integration
List of Rust software and tools
List_of_Rust_software_and_tools
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Dependence_analysis
Concept in computer science
) {\displaystyle h(\ell )} and h ′ ( ℓ ) {\displaystyle h'(\ell )} is undefined). The logic allows to prove judgements of the form s , h ⊨ P {\displaystyle
Separation_logic
Computer science field
to TLA+, that uses Python-like specification language, that has both behavioral modeling like TLA+ and probabilistic modeling like PRISM ISP code level
Model_checking
Macros whose expansion is guaranteed not to cause the capture of identifiers
standard functions and operators, globally or locally, as invoking undefined behavior. Such usage can be thus diagnosed by the implementation as erroneous
Hygienic_macro
Computer program for the Boolean satisfiability problem
proving unsatisfiability, and others at finding solutions. All of these behaviors can be seen in the SAT solving contests. Parallel SAT solvers come in
SAT_solver
Object that enables processing collection items in order
so); using an invalidated iterator is an error that will lead to undefined behavior, and such errors need not be signaled by the run time system. Implicit
Iterator
Overview of and topical guide to Rust
development[user-generated source?] Memory-safe language – prevents common undefined behavior like dangling pointers and buffer overflows Graydon Hoare – creator
Outline of the Rust programming language
Outline_of_the_Rust_programming_language
Free and open-source Unix-like operating system
of in-kernel bug detection facilities, including code sanitizers (undefined behavior, address, thread, memory sanitizers), a kernel memory disclosure detection
NetBSD
Point in a computer program where instruction-execution begins
simply continue executing beyond the end of the program, resulting in undefined behavior. Usually, there is not a single exit point specified in a program
Entry_point
Replacing a number with a simpler value
is increased by 2 each time the Table-maker's dilemma occurs (with undefined behavior in the very unlikely event that some limit of the machine is reached)
Rounding
Approach to static program analysis
abstraction. A semantics is a mathematical characterization of a possible behavior of the program. The most precise semantics, describing very closely the
Abstract_interpretation
An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been declared by that code. In some
Undefined_variable
Set of software engineering methods
Polyvariance Rice's theorem Runtime verification Safety and liveness Undefined behavior Semantics Types Axiomatic Denotational Categorical semantics Operational
Program_slicing
Object with no referenced value or with defined neutral ("null") behavior
place-holder, but may not be used for direct dispatch: a->makeSound() is undefined behavior if a is a null pointer. The null object pattern solves this problem
Null_object_pattern
Research operating system from Microsoft Research
cannot violate type or memory safety, and thus cannot directly cause undefined behavior. If it attempts to make invalid requests to the Nucleus, formal verification
Verve_(operating_system)
Datatype in C++
same object as that pointer, where this is possible without invoking undefined behavior. This equivalence is a reflection of the typical implementation, which
Reference_(C++)
List of x86 microprocessor instructions
zero – for which TZCNT returns input operand size, but BSF produces undefined behavior (leaves destination unmodified on most modern CPUs). For BEXTR, the
List_of_x86_instructions
Computer mechanism
needing to terminate the application holding them. This can cause an undefined behavior, since the program will receive an unexpected error when using the
File_locking
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
Girl/Female
Tamil
Nature, Behavior
Surname or Lastname
English
English : nickname for a person who insisted on a strict code of social behavior.German : topographic name for someone who lived on or by a hill, from Middle High German stickel ‘hill’, ‘slope’ + the suffix -er denoting an inhabitant; in the south an occupational name for someone who shapes and sets stakes in vineyards.
Girl/Female
Hindu
Truth, Morality, Justice, Good behavior
Girl/Female
Arabic, Muslim
Writer; Stated; Well-defined
Boy/Male
Indian
Behavior
Boy/Male
Muslim
Behavior
Girl/Female
Muslim
Writer, Stated, Well-defined
Girl/Female
Hindu
Nature, Behavior
Girl/Female
Hindu, Indian, Marathi, Tamil
Beauty Redefined
Girl/Female
Hindu
Truth, Morality, Justice, Good behavior
Girl/Female
Tamil
Truth, Morality, Justice, Good behavior
Boy/Male
Tamil
Behavior
Girl/Female
Afghan, Arabic, Australian, Iranian, Muslim, Parsi
Star; Venus; The Planet Venus; Immaculate; Undefiled; Planet Venus
Girl/Female
Tamil
Nature, Behavior
Boy/Male
Hindu
Well defined body
Boy/Male
Tamil
Well defined body
Girl/Female
Hindu
Truth, Morality, Justice, Good behavior
Girl/Female
Tamil
Truth, Morality, Justice, Good behavior
Girl/Female
Tamil
Beauty redefined
Girl/Female
Tamil
Truth, Morality, Justice, Good behavior
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
Boy/Male
American, Anglo, British, English
Dweller at the Ash Tree; Foreigner
Boy/Male
Gujarati, Hindu, Indian, Jain, Kannada, Kashmiri, Malayalam, Marathi, Parsi, Punjabi, Sikh, Traditional
Brave; A Brave Person
Girl/Female
Hindu
System, Organization
Girl/Female
Hindu
Happiness
Surname or Lastname
English (mainly central southern England and South Wales)
English (mainly central southern England and South Wales) : topographic name for someone who lived by a path across a heath, from Middle English hathe ‘heath’ + weye ‘way’.from an (apparently rare) Old English female personal name, Heaðuwīg, composed of the elements heaðu ‘strife’, ‘contention’ + wīg ‘war’.
Boy/Male
Hindu, Indian
Lord Vishnu
Boy/Male
Bengali, Hindu, Indian, Traditional
Servant of the God
Female
Norse
Old Norse name composed of the elements gunnr "war" and varr "cautious, vigilant," hence "war-vigilant."
Girl/Female
Indian
Purity, Clarity, Serenity
Girl/Female
Hindu
Daughter of Goddess Lakshmi (Daughter of Goddess Lakshmi)
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
UNDEFINED BEHAVIOR
n.
Unrefined or raw sugar.
n.
Unlimited; not bounded or restricted; undefined.
a.
Undefiled.
adv.
In an irresolute, undecided, or hesitating manner.
n.
Undefined quantity; extent; degree.
n.
Any portion of territory of undefined extent; a region; a country; a tract.
a.
Unviolated; uninjured; undefiled; uncorrupted.
a.
Not accomplished or performed; unfinished; also, deficient in accomplishment; unrefined.
v. t.
To make indefinite; to obliterate or confuse the definition or limitations of.
a.
Pure; undefiled.
n.
Undecided character of a disease.
a.
Without stain or blemish; spotless; undefiled; clear; pure.
a.
Pure; undefiled; unmixed; fresh; new; as, virgin soil; virgin gold.
adv.
At a time undefined; once in a while; now and then; sometimes.
a.
Undefined; indefinite; not bounded by proper exceptions; as, unlimited terms.
a.
Not blemished; undefiled; pure.
n.
An undecided, inquiring state of mind; doubt; uncertainty.
n.
A thing defined or determined.
a.
Gross; low; unrefined.
imp. & p. p.
of Define