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

Input-output techniques, After going through details of device interfaces n...

After going through details of device interfaces next point to be discussed is how the interface can be used to support I/O from devices. Binary information received from an extern

Determine the o/p for JK flip flop with J=1 & K=0, For JK flip flop with J=...

For JK flip flop with J=1, K=0, the output after clock pulse will be ? Ans. The output will be 1 after clock pulse.

Why floating point numbe process than integer, Why floating point number mo...

Why floating point number more difficult to represent and process than integer? In floating point numbers we have to show any number in three fields sign, exponent and mantissa

Real-time systems and control, A group report with no more than three stude...

A group report with no more than three students per group is to be handed in to explain your design procedures and simulation results. Representative graphical system outputs (clea

What are the main data structures used in rdbms, What are the main data str...

What are the main data structures used in the following areas: RDBMS, Network data model and Hierarchical data model? RDBMS = Array (i.e. Array of structures) Network data m

Why erlang is used, Erlang is used to (A) Measure busy period         ...

Erlang is used to (A) Measure busy period                (B) Give total busy period in minutes (C)  Measure average call rate       (D) Indicate total call period Ans

Advantages of edi (electronic data interchange), Advantages of EDI 1.  ...

Advantages of EDI 1.  EDI replaces paper transactions with electronic transactions therefore it saves times and speeds up transactions. 2.  It gives a legal record of busine

Translate the sentences into predicate calculus, Translate each of the foll...

Translate each of the following sentences into predicate calculus, conceptual dependencies, and conceptual graphs: 1. Bill sold the book to the book store." 2. "John borrowed

Types of pipelines - computer architecture, Types of Pipelines: Instr...

Types of Pipelines: Instructional pipeline  It is used where different stages of an instruction fetch and execution take place in a pipeline. Arithmetic pipeline

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