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

Universal serial bus - computer architecture, Universal Serial Bus - comput...

Universal Serial Bus - computer architecture: USB   Universal Serial Bus   Speed Low-speed(1.5 Mb/s) High-speed(480 Mb/s) Full-speed(12 Mb/s)   De

Face detection, i want the matlab code for the following events 1. face det...

i want the matlab code for the following events 1. face detection 2. video to frame conversion 3.video shot boundary detection

Explain about decimal numbers, Q. Explain about Decimal Numbers? Deci...

Q. Explain about Decimal Numbers? Decimal number system has 10 digits signified by 0,1,2,3,4,5,6,7,8 and 9. Any decimal number can be signified as a string of these digits an

A* search - artificial intelligence, A* Search - artificial intelligence: ...

A* Search - artificial intelligence: A* search in the combines is the best parts of uniform cost search, namely the fact that it's optimal and complete, and the other best par

The concept of program-parallel computing, The Concept of Process Infor...

The Concept of Process Informally, a method is a program in execution, behind the program has been loaded in the main memory. However, a method is more than just a program code

What are the types of instructions, Q. What are the types of Instructions? ...

Q. What are the types of Instructions? Computer instructions are translation of high level language code to machine level language programs. So from this point of view machine

What is electronic data interchange, What is Electronic Data Interchange? ...

What is Electronic Data Interchange? Electronic Data Interchange (EDI): It is used by organizations for transactions which arise on regular basis to a pre-found format.

Pruning - artificial intelligence, Pruning - artificial intelligence: ...

Pruning - artificial intelligence: Recall which pruning a search space means deciding that there certain branches to should not be explored. Moreover if an agent knows for sur

What are priority queues, What are priority Queues? There are many queu...

What are priority Queues? There are many queues in which we can insert items or delete items from any of the position based on some property. Now, those queues based on the pro

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