Software Constant Value

A Software Constant Value is a software variable with a constant value.

• AKA: Constant (Computer Programming).
• See: Characters Per Line, Computer Programming, Identifier (Computer Programming), Value (Computer Science), Computer Program, Self-Modifying Code, Memory Location, Variable (Computer Science), Self-Documenting, Correctness (Computer Science), Compile-Time, Run Time (Program Lifecycle Phase), Compiler Optimization.

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References

2015

• (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/Constant_(computer_programming) Retrieved:2015-2-13.
  • In computer programming, a constant is an identifier with an associated value which cannot be altered by the program during normal execution – the value is constant. This is contrasted with a variable, which is an identifier with a value that can be changed during normal execution – the value is variable. Constants are useful for both programmers and compilers: for programmers they are a form of self-documenting code and allow reasoning about correctness; while for compilers they allow compile-time and

     run-time checks that constancy assumptions are not violated, and allow or simplify some compiler optimizations.

    There are various specific realizations of the general notion of a constant, with subtle distinctions that are often overlooked. The most significant are: compile-time (statically-valued) constants, run-time (dynamically-valued) constants, immutable objects, and constant types (const).

    Typical examples of compile-time constants include mathematical constants, values from standards (here maximum transmission unit), or internal configuration values (here characters per line), such as these C examples:
    <source lang=c>
    const float PI = 3.1415927; // maximal single float precision
    const unsigned int MTU = 1500; // Ethernet v2, RFC 894
    const unsigned int COLUMNS = 80; </source> Typical examples of run-time constants are values calculated based on inputs to a function, such as this C++ example:
    <source lang=cpp> void f(std::string s) {
    const size_t l = s.length();
    // ...
    } </source>

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