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

Highly encoded micro-instructions, Highly Encoded micro-instructions ...

Highly Encoded micro-instructions Encoded bits required in micro-instructions are small. It provided an aggregated view that is a higher view of CPU as just an encoded

Dialog-task updates, Dialog-task updates are Synchronous updates.

Dialog-task updates are Synchronous updates.

Sorting, Different sorting algorithm will be discussed in the lecutres. The...

Different sorting algorithm will be discussed in the lecutres. The task in this worksheet is to write a funtions based on the Quicksort algorithm. When sorting an array of objec

Online teaching jobs, Dear, I''m an engineering post graduate in computer s...

Dear, I''m an engineering post graduate in computer science. I would like to work as online tutor. please suggest ideas. Thank You.

Support concurrent programming, Q) a.Define the programming-language featur...

Q) a.Define the programming-language features that are required to properly  support concurrent programming? b. What support do these features need from the operating system?

What is a parallel port, What is a parallel port? A parallel port trans...

What is a parallel port? A parallel port transfers data in the form a number of bits, typically 8 to 16, concurrently to or from the device.

Row-major order and column-major order of arrays, Two-dimensional array is ...

Two-dimensional array is represented in memory in following two ways: 1.  Row major representation: To attain this linear representation, the first row of the array is kept in

Define thread cancellation and target thread, Define thread cancellation & ...

Define thread cancellation & target thread.  The thread cancellation is the task of terminating a thread before it has done. A thread that is to be cancelled is often referred

What is batch processing, What is Batch processing In this process, a n...

What is Batch processing In this process, a number of tasks (or jobs) are all collected together over a set period of time. They are then all loaded into the computer system (i

Micrography technology, Micrography: Micrographic technology is an out...

Micrography: Micrographic technology is an outgrowth of photographic technology. Since this technology is being increasingly used to supplement computer systems, strong electr

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