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

What do understand by the granularity of a parallel system, What do underst...

What do understand by the granularity of a parallel system ? Granularity refers to the quantity of computation complete in parallel relative to the size of the entire program. I

Order in which filters get implemented, If we have multiple filters implet...

If we have multiple filters impleted, what is the order in which these filters get implemented?   Ans) 1. Authorization filters 2. Response filters 3. Action filters

Computer science, Read in integers until a zero is read in. Keep a total o...

Read in integers until a zero is read in. Keep a total of both the quantity and the sum of the negative integers and the positive integers. Once a zero is read in (signifying the

Steps in building the structure chart, Steps in Building the Structure Char...

Steps in Building the Structure Chart 1. Recognize top level modules and decompose them into lower levels 2. Add control connections 3. Add couples 4. Review and revis

Computer architecture, describe the block diagram of a system showing the f...

describe the block diagram of a system showing the following microprocessor memory system buses

Mutation - canonical genetic algorithm, Mutation: However it may appea...

Mutation: However it may appear that the above recombinations are a little arbitrary that especially as points defining whether crossover and inversion occur are chosen random

Determine the handles data rate of broad band isdn, Broad Band ISDN handles...

Broad Band ISDN handles data rate of about (A) 64 kbps                                      (B) 100 mbps (C) 5.4 mbps                                    (D) 2.048 mbps

What do you mean by mouse protocols, Q. What do you mean by Mouse Protocols...

Q. What do you mean by Mouse Protocols? Mouse protocol is the digital code to that signal from the mouse gets converted. There are four main protocols: Microsoft, Mouse Systems

Calculate the switching elements in a two stage network, In a two stage ne...

In a two stage network there are 512 inlets and outlets, r=s=24. If the probability that a given inlet is active is 0.8, calculate: the switching elements Given: N =M =512,

Differentiate between protected and real modes of an intel, Differentiate b...

Differentiate between protected and real modes of an Intel microprocessor Operation of Real mode interrupt: When microprocessor completes executing the current instruction, it

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