In computing, aliasing is a term that generally means that one variable or some reference, when changed, has an indirect (usually unexpected) effect on some other data. Originally, the word computing was synonymous with counting and calculating, and a computer was a person who computes. ...

For example, the C programming language does not perform array bounds checking. One can then exploit the implementation of the programming language by the compiler, plus the computer architecture's assembly language conventions, to achieve aliasing effects. The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a low-level standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the...

If an array is created on the stack, with a variable laid out in memory directly beside that array, one could index outside that array and then directly change that variable by changing the relevant array element. For example, if we have a int array of size ten (for this example's sake, calling it vector), next to another int variable (call it i), vector[11] would be aliased to i if they are adjacent in memory. The word stack can mean several different things: Noun Stack (geology): Coastal landform - A large vertical column of rock in the sea. ... In computer programming, an array, also known as a vector or list, is one of the simplest data structures. ...

This is possible in some implementations of C because an array is in reality a pointer to some location in memory, and array elements are merely offsets off that memory location. Since C has no bounds checking, indexing and addressing outside of the array is possible. Note that the aforementioned aliasing behaviour is implementation specific. Some implementations may leave space between arrays and variables on the stack, for instance, to minimize possible aliasing effects. C programming language specifications do not specify how data is to be laid out in memory.

Controlled aliasing behaviour may be desirable in some cases (that is, aliasing behaviour that is specified, unlike the aliasing behaviour in C). The Perl programming language specifies, in some constructs, aliasing behaviour, such as in foreach loops. This allows certain data structures to be modified directly with less code. For example, Programming Republic of Perl logo Perl, also Practical Extraction and Report Language (a backronym, see below), is a programming language released by Larry Wall on December 18, 1987 that borrows features from C, sed, awk, shell scripting (sh), and (to a lesser extent) from many other programming languages. ... An alternate rewrite has been has been proposed. ...

 @x = (1, 2, 3); foreach $e (@x) { $e++ } print "@xn"; 

will print out "2 3 4" as a result. If one would want to bypass aliasing effects, one would copy the contents of the index variable into another and change the copy.