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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 other languages such a usage is considered to be sufficiently ...
C and C++ distinguish implementation-defined behavior from unspecified behavior. For implementation-defined behavior, the implementation must choose a particular behavior and document it. An example in C/C++ is the size of integer data types. The choice of behavior must be consistent with the documented behavior within a given execution of the ...
In C and C++, the line above represents a forward declaration of a function and is the function's prototype.After processing this declaration, the compiler would allow the program code to refer to the entity printThisInteger in the rest of the program.
It is the responsibility of the programmer to write code that never invokes undefined behavior, although compiler implementations are allowed to issue diagnostics when this happens. Compilers nowadays have flags that enable such diagnostics, for example, -fsanitize=undefined enables the "undefined behavior sanitizer" in gcc 4.9 [2] and in clang ...
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]
A global identifier is declared outside of functions and is available throughout the program. A local identifier is declared within a specific function and only available within that function. [1] For implementations of programming languages that are using a compiler, identifiers are often only compile time entities.
Another example can be when dealing with structs. In the code snippet below, we have a struct student which contains some variables describing the information about a student. The function register_student leaks memory contents because it fails to fully initialize the members of struct student new_student.
By reserving the terms, they can be implemented in future versions of Java, if desired, without breaking older Java source code. For example, there was a proposal in 1999 to add C++-like const to the language, which was possible using the const word, since it was reserved but currently unused; however, this proposal was rejected – notably ...