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Not only are uninitialized variables a frequent cause of bugs, but this kind of bug is particularly serious because it may not be reproducible: for instance, a variable may remain uninitialized only in some branch of the program. In some cases, programs with uninitialized variables may even pass software tests.
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. [1]In some programming languages, an implicit declaration is provided the first time such a variable is encountered at compile time.
In mathematics, the term undefined refers to a value, function, or other expression that cannot be assigned a meaning within a specific formal system. [1]Attempting to assign or use an undefined value within a particular formal system, may produce contradictory or meaningless results within that system.
This is an accepted version of this page This is the latest accepted revision, reviewed on 6 February 2025. Language for communicating instructions to a machine The source code for a computer program in C. The gray lines are comments that explain the program to humans. When compiled and run, it will give the output "Hello, world!". A programming language is a system of notation for writing ...
By definition, the runtime can assume that undefined behavior never happens; therefore, some invalid conditions do not need to be checked against. For a compiler , this also means that various program transformations become valid, or their proofs of correctness are simplified; this allows for various kinds of optimizations whose correctness ...
In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. [1] Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions. [1]
int foo; //foo might be defined somewhere in this file extern int bar; //bar must be defined in some other file In Pascal and other Wirth programming languages, it is a general rule that all entities must be declared before use, and thus forward declaration is necessary for mutual recursion, for instance.
Dominance frontiers define the points at which Φ functions are needed. In the above example, when control is passed to node 4, the definition of result used depends on whether control was passed from node 2 or 3. Φ functions are not needed for variables defined in a dominator, as there is only one possible definition that can apply.