Define external variable declaration, Computer Engineering

Assignment Help:

Summarize the distinction between an external variable definition and an external variable declaration.

When we have ''declared'' a variable, we have meant that we have told the compiler about the variable; i.e. its type and its name, as well as allocated a memory cell for the variable (either locally or globally). This latter action of the compiler, allocation of storage, is more properly called the definition of the variable. The stricter definition of declaration is simply to describe information ''about'' the variable.  For automatic and register variables, there is no difference between definition and declaration. The process of declaring an automatic or a register variable defines the variable name and allocates appropriate memory. However, for external variables, these two operations may occur independently. This is important because memory for a variable must be allocated only once, to ensure that access to the variable always refers to the same cell.

If an external variable is to be used in a file other than the one in which it is defined, a mechanism is needed to ''connect'' such a use with the uniquely defined external variable cell allocated for it. This process of connecting the references of the same external variable in different files, is called resolving the references.

External  variables  may  be  defined  and  declared  with  a  declaration  statement outside any function, with no storage class specifier. Such a declaration allocates memory for the variable. A declaration statement may also be used to simply declare a variable name with the extern storage class specifier at the beginning of the declaration. Such a declaration specifies that the variable is defined elsewhere, i.e. memory for this variable is allocated in another file. Thus, access to an external variable in a file other than the one in which it is defined is possible if it is declared with the keyword extern; no new memory is allocated. Such a  declaration tells  the compiler  that  the  variable  is  defined  elsewhere,  and  the code  is compiled with the external variable left unresolved. The reference to the external variable is resolved during the linking process

 


Related Discussions:- Define external variable declaration

Evidence of intelligent behavior - artificial intelligence, Evidence of int...

Evidence of intelligent behavior - Artificial Intelligence: Machines mean they could simply be personal computers, or they could be robots with embedded automative systems, or

Adding xml files to your page, Step 1: Choose File -> Import XML into Templ...

Step 1: Choose File -> Import XML into Template Step 2: Select the XML file & click Open When an XML file is imported, Dreamweaver merges XML content in Template, which is be

Explain common control, Explain Common Control. Common Control: Those...

Explain Common Control. Common Control: Those systems wherein the control subsystem is outside the switching network are termed as common control switching system. Therefore,

What are the different scheduling policies in linux, What are the different...

What are the different scheduling policies in Linux The Linux scheduler has three different scheduling policies: one for 'normal'Processes, and two for 'real time' processes

State the various security tools, State the various Security Tools Sec...

State the various Security Tools Securing an Intranet is not a simple task. Just as articles in a house are protected by use of various types of security systems such as lock

Why spc is used, SPC is used for (A)  Carrying Exchange Control Functi...

SPC is used for (A)  Carrying Exchange Control Functions (B)  Carrying Subscriber Control Functions (C)  Exchange Hardware (D)  Signalling Purpose Ans:

Define cloud computing with example, Define Cloud Computing with example. ...

Define Cloud Computing with example. Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., se

Computer Architecture, As an advocate of CISC architecture to RISC architec...

As an advocate of CISC architecture to RISC architecture, what are the merits and demerits of CISC to RISC architecture

Adding layers to the timeline, ADDING LAYERS TO THE TIMELINE AND GIVING MOT...

ADDING LAYERS TO THE TIMELINE AND GIVING MOTION TO THE LAYER Step 1:  Choose Layer from Common toolbar after that draw a layer. Step 2:  Write the text inside Layer. Step

Describe session handling in a web farm, Describe session handling in a web...

Describe session handling in a web farm, how does it work and what are the limits ?   In ASP.NET there are three ways to handle session objects. Single support the in-proc mec

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd