Đề Xuất 2/2023 # What Are The Differences Between A Pointer Variable And A Reference Variable In C++? # Top 10 Like | Cuocthitainang2010.com

Đề Xuất 2/2023 # What Are The Differences Between A Pointer Variable And A Reference Variable In C++? # Top 10 Like

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The direct answer

What is a reference in C++? Some specific instance of type that is not an object type.

What is a pointer in C++? Some specific instance of type that is an object type.

From the ISO C++ definition of object type:

An object type is a (possibly cv-qualified) type that is not a function type, not a reference type, and not cv void.

It may be important to know, object type is a top-level category of the type universe in C++. Reference is also a top-level category. But pointer is not.

Pointers and references are mentioned together in the context of compound type. This is basically due to the nature of the declarator syntax inherited from (and extended) C, which has no references. (Besides, there are more than one kind of declarator of references since C++ 11, while pointers are still “unityped”: &+&& vs. *.) So drafting a language specific by “extension” with similar style of C in this context is somewhat reasonable. (I will still argue that the syntax of declarators wastes the syntactic expressiveness a lot, makes both human users and implementations frustrating. Thus, all of them are not qualified to be built-in in a new language design. This is a totally different topic about PL design, though.)

Otherwise, it is insignificant that pointers can be qualified as a specific sorts of types with references together. They simply share too few common properties besides the syntax similarity, so there is no need to put them together in most cases.

Note the statements above only mentions “pointers” and “references” as types. There are some interested questions about their instances (like variables). There also come too many misconceptions.

The differences of the top-level categories can already reveal many concrete differences not tied to pointers directly:

Object types can have top-level cv qualifiers. References cannot.

Variable of object types do occupy storage as per the abstract machine semantics. Reference do not necessary occupy storage (see the section about misconceptions below for details).

A few more special rules on references:

Compound declarators are more restrictive on references.

References can collapse.

Special rules on && parameters (as the “forwarding references”) based on reference collapsing during template parameter deduction allow “perfect forwarding” of parameters.

References have special rules in initialization. The lifetime of variable declared as a reference type can be different to ordinary objects via extension.

BTW, a few other contexts like initialization involving std::initializer_list follows some similar rules of reference lifetime extension. It is another can of worms.

The misconceptions

I know references are syntactic sugar, so code is easier to read and write.

Technically, this is plain wrong. References are not syntactic sugar of any other features in C++, because they cannot be exactly replaced by other features without any semantic differences.

(Similarly, lambda-expressions are not syntactic sugar of any other features in C++ because it cannot be precisely simulated with “unspecified” properties like the declaration order of the captured variables, which may be important because the initialization order of such variables can be significant.)

C++ only has a few kinds of syntactic sugars in this strict sense. One instance is (inherited from C) the built-in (non-overloaded) operator [], which is defined exactly having same semantic properties of specific forms of combination over built-in operator unary * and binary +.

Storage

So, a pointer and a reference both use the same amount of memory.

The statement above is simply wrong. To avoid such misconceptions, look at the ISO C++ rules instead:

From [intro.object]/1:

… An object occupies a region of storage in its period of construction, throughout its lifetime, and in its period of destruction. …

From [dcl.ref]/4:

It is unspecified whether or not a reference requires storage.

Note these are semantic properties.

Pragmatics

Even that pointers are not qualified enough to be put together with references in the sense of the language design, there are still some arguments making it debatable to make choice between them in some other contexts, for example, when making choices on parameter types.

But this is not the whole story. I mean, there are more things than pointers vs references you have to consider.

If you don’t have to stick on such over-specific choices, in most cases the answer is short: you do not have the necessity to use pointers, so you don’t. Pointers are usually bad enough because they imply too many things you don’t expect and they will rely on too many implicit assumptions undermining the maintainability and (even) portability of the code. Unnecessarily relying on pointers is definitely a bad style and it should be avoided in the sense of modern C++. Reconsider your purpose and you will finally find that pointer is the feature of last sorts in most cases.

Sometimes the language rules explicitly require specific types to be used. If you want to use these features, obey the rules.

Copy constructors require specific types of cv-& reference type as the 1st parameter type. (And usually it should be const qualified.)

Move constructors require specific types of cv-&& reference type as the 1st parameter type. (And usually there should be no qualifiers.)

Overloaded operator= as special member functions requires reference types similar to 1st parameter of copy/move constructors.

Postfix ++ requires dummy int.

If you know pass-by-value (i.e. using non-reference types) is sufficient, use it directly, particularly when using an implementation supporting C++17 mandated copy elision. (Warning: However, to exhaustively reason about the necessity can be very complicated.)

If you want to operate some handles with ownership, use smart pointers like unique_ptr and shared_ptr (or even with homebrew ones by yourself if you require them to be opaque), rather than raw pointers.

If you are doing some iterations over a range, use iterators (or some ranges which are not provided by the standard library yet), rather than raw pointers unless you are convinced raw pointers will do better (e.g. for less header dependencies) in very specific cases.

If you know pass-by-value is sufficient and you want some explicit nullable semantics, use wrapper like std::optional, rather than raw pointers.

If you know pass-by-value is not ideal for the reasons above, and you don’t want nullable semantics, use {lvalue, rvalue, forwarding}-references.

Even when you do want semantics like traditional pointer, there are often something more appropriate, like observer_ptr in Library Fundamental TS.

The only exceptions cannot be worked around in the current language:

When you are implementing smart pointers above, you may have to deal with raw pointers.

Specific language-interoperation routines require pointers, like operator new. (However, cv-void* is still quite different and safer compared to the ordinary object pointers because it rules out unexpected pointer arithmetics unless you are relying on some non conforming extension on void* like GNU’s.)

Function pointers can be converted from lambda expressions without captures, while function references cannot. You have to use function pointers in non-generic code for such cases, even you deliberately do not want nullable values.

So, in practice, the answer is so obvious: when in doubt, avoid pointers. You have to use pointers only when there are very explicit reasons that nothing else is more appropriate. Except a few exceptional cases mentioned above, such choices are almost always not purely C++-specific (but likely to be language-implementation-specific). Such instances can be:

You have to serve to old-style (C) APIs.

You have to meet the ABI requirements of specific C++ implementations.

You have to interoperate at runtime with different language implementations (including various assemblies, language runtime and FFI of some high-level client languages) based on assumptions of specific implementations.

You have to improve efficiency of the translation (compilation & linking) in some extreme cases.

You have to avoid symbol bloat in some extreme cases.

Language neutrality caveats

If you come to see the question via some Google search result (not specific to C++), this is very likely to be the wrong place.

References in C++ is quite “odd”, as it is essentially not first-class: they will be treated as the objects or the functions being referred to so they have no chance to support some first-class operations like being the left operand of the member access operator independently to the type of the referred object. Other languages may or may not have similar restrictions on their references.

References in C++ will likely not preserve the meaning across different languages. For example, references in general do not imply nonnull properties on values like they in C++, so such assumptions may not work in some other languages (and you will find counterexamples quite easily, e.g. Java, C#, …).

There can still be some common properties among references in different programming languages in general, but let’s leave it for some other questions in SO.

(A side note: the question may be significant earlier than any “C-like” languages are involved, like ALGOL 68 vs. PL/I.)

What’S The Difference Between Mrs., Ms. And Miss?

Here’s how to use the three prefixes.

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Now that you’re getting married, it’s officially time to learn the difference between the prefixes Mrs., Ms. and Miss. Why? Because you’re addressing wedding invitations-not to mention the fact that yours may be changing. To clear all confusion, we’re explaining exactly when and how to use each title. Consider this the official guide to Ms. vs. Mrs. vs. Miss.

What’s the difference between Mrs., Ms. and Miss?

Historically, “Miss” has been the formal title for an unmarried woman. “Mrs.,” on the other hand, refers to a married woman. “Ms.” is a little trickier: It’s used by and for both unmarried and married women.

Will I be Ms. or Mrs. after I get married?

Ms. vs. Mrs.-which should you choose? In short, it depends. Typically, brides who change their name postwedding go by “Mrs.” after marriage, since it usually indicates that they’re sharing a surname with their spouse (as in “Mr. and Mrs. Smith”). If you’re keeping your maiden name, you can go by “Ms.” instead, or stick with “Mrs.” as in “Mr. Smith and Mrs. Brown.” You can also go by “Ms.” if you’d rather your title of respect not be associated with your marital status at all.

Changing your last name? Make the process way easier by signing up for a name-change service. HitchSwitch autofills most of the paperwork, which-trust us-is worth the saved time.

Miss, Mrs. or Ms.: Which should I write on wedding invitations?

If a guest is a child, feel free to use “Miss.” If she’s an unmarried adult, go with “Miss” or “Ms.” (Note that “Ms.” is often preferred for older [thirty and up] women). If she’s married and you know her chosen title, write that. If you’re unsure, “Ms.” is a safe and appropriate choice. Check out our complete guide to addressing wedding invitations for more specific scenarios.

Ready to buy your invitations or save-the-dates? We love Minted for affordable stationery, Shutterfly for photo paper goods and Etsy for handmade items. Or, work with a local vendor for extra-bespoke cards.

What Is The Difference Between Job Career And Profession?

I am an employment counselor. Well, you can call me a career counselor, as most of people consider me to be it!

This is what that made me to write this post!

Why is Job Different from Career?

During your course of a career, you would be doing numerous different jobs. I hope this line makes a clear demarcation between the two.

What is a Job?

A job is a task or practice that is done to earn money. It is not your career, but yes an integral part of your career. It is because the type of job you are doing presently will be influencing your future career path.

So, when you decide on a career path, you look for different jobs within its circumference. You go to an interview, decide about the salary, and end up having the job. Hence, the tasks you are doing at that particular time is your job.

Probably, in the next 5 years, you would not be doing the current job. But will have the same career path and goal.

What is a Career?

When you do a series of connected job or employment options one after the other, then this builds up your career path. Your career is not one job, but the series of jobs. During the course of your career, you are building up skills and moving higher to earn more bucks. At the same time, you gain skills ideal to cater the prestigious employment opportunities.

In the next few years, you would have the same career and do the same thing. But things will be different!

You will have more interesting challenges to handle, in-depth knowledge about the specific field, and better earnings to take back home.

Perhaps you can have a better understanding glancing at some differences between the two.

Difference Between Career and Job:

Dependency:

Your current job might have or might not have a relation to your future job. It can be completely unrelated to tasks you will be doing in the future.

Your career is heavily dependent on the types of jobs you are doing at the present time. Also, it is equally influential with the jobs you do in the future time.

For example, you might be a clerk earlier. After that, you completed the graduation and now opted for an executive position in a reputed organization. You see your past job does not have any relation to your current job.

But if you glance at your career chart then there is a great improvement. You have moved in an upward direction. This confirms that you are now in a better position and earning more than before.

Also, what you are doing presently will affect your future career graph!

Functionality:

Why are you doing that job? Not because you wanted to do it, but mainly to make some easy cash in your hand.

Even if you are a highly qualified person, but if you are not getting hired to a reputed company then what choice you have! You would agree to do a low – profile job. It is because earning money is the main need of time. And this could be fulfilled only with a job.

But if I talk about your career then it is a series of such jobs. The types of jobs you do will frame your career. It is totally up to you, how you plan your career to be.

A good career is one with an upward moving graph. A bad career is one if your career graph is moving in a downward direction.

Networks build during a job might not be long-lasting. The people you meet at a job might not relate to you in the future. They may not be the same people you meet in your next job.

But networks build during a career are lasting and reliable. Your career will offer you with numerous networking opportunities. Since most of the people would have the same career, so they will keep in touch with you now and then again.

Getting a job does not require any planning. Rather you need a set of skills and efficiency to get the specific task done.

The skills you possess in your career are those learned and developed during the job. This can be individualized learning or any special training.

Let me clear this with an example. You were once a beautician doing the basic salon tasks. Later on, you opened your own salon. When you got your first job then you might not possess the skills needed. But you gain them over time. The skills you learned during your job have helped to shape your career. As a result, you are presently successful and earning more.

So, your job shifted from a salon worker to a salon owner. But both of them together will define your career journey.

A job holds external risks. It is safe and stable in most of the cases in terms of earning. Although there can be shifting priorities, things get settled if you are good at your job.

Some external risks involved in a job are altering the demand, relocation, or changes in the work schedule. You can never plan the risks to take. They come from various external factors.

On the other hand, a career might not be stable. It is because it involves taking lots of risks. You may have both internal and external risks involved in your career. But you can always plan the risks to take. Also, you can prepare a backup plan to overcome the risk without experiencing much loss.

Well, I hope you have got a good idea about the difference between ‘job’ and ‘career.’ But I would like to ask you one thing. What is the difference between a career and a profession?

Like you, most of my clients have the same confusion. So, in the next section of my post, I would like to elaborate on this subject further.

Career and Profession:

You might be using the two terms interchangeably. But let me tell you that you are making a huge mistake! Just like a job and career, there is a subtle difference between a career and a profession.

What is Career in Context of Profession?

I have already detailed about what is the basic definition of a career. This section will help you understand better about a career in the context of the profession! A career could imply,

It is also related to the progress of the person or the achievement during his course of action through life. Your career can be in line with some undertaking or profession.

For example, she was a missionary nurse who spent much of her career in the United States.

What is a Profession?

The profession is a term derived from the Latin word ‘profiteering.’ It means declaring publicly.

The precise definition of a profession is considering it as a vocation identified with specialized training and educational knowledge. The core purpose of the profession is to offer an objective to the person.

A person performs specialized services to others, within a profession. This service can be against direct or indirect remuneration. Besides monetary gains, a person expects to achieve lasting business gains with his profession.

Hence, concisely speaking, the profession is an occupation in exchange for money that requires formal qualification as well as long training.

For example, she selected the profession of teaching. He is a painter by profession.

This does not define whether he is successful or unsuccessful in his course of work. But the profession defines the service you can offer to others. In order to become a professional, you need to possess specialized skills and traits.

Difference Between Profession and Career:

A career may or may not involve the need for formal education or special training. It is shaped over the course of time and is followed by the overall life work of an individual. A profession demands a person to have a set of skills. If you want to be a professional then you need to have something exclusive to you. Might be, you require formal training and qualifications to become a professional.

Field of job

Your career can involve jobs belonging to different fields and niches. Even most people have a career involving mixed jobs. Your jobs can involve different skills and services that you would be offering during your job role.

But in a profession, you are always offering one specialized service. For example, you can have a profession as a doctor, chartered accountant, engineer, and other such divisions. Under such subjects, you are offering only one specific service.

Promotions or Advancement:

Scope of Measurement:

The profession is defined as the specific field of performing a specialized role. It is not a job that can measure in figures. For instance, you are a doctor by profession, but presently not practicing it. This will imply that you have no job or you are presently unemployed. But this will not change your profession.

Alternatively, it is possible to measure a career. If you are doing better than your past position then you have a better career. But if the case is alternate then you are not having a favorable career. Hence, you can measure the career to some extent.

Comparison Chart:

Job vs. Career vs. Profession:

There is a very thin line of difference between a job, career, and profession. This I would like to explain with an example.

You are a Chartered Accountant who was working for the past 5 years with a reputed organization in Europe. But presently you have some family responsibilities. Hence, you are not rendering your service at all.

Your job was your 5 years of working where you were involved with an organization. During that course of time, you were performing a task in exchange for money.

Your profession is Chartered Accountancy. You have undertaken specialized education and training to begin your profession.

Your career was at a good pace when you were actively involved in a job. But presently you are not working, so your career can be considered stagnant. However, this will not alter your profession. As you can always begin working again as a Chartered Accountant sometime in the near future.

Tips for Job:

Your job would always demand you to perform the given task efficiently and within the desired time-frame.

Investing the desired emotional, mental, and physical energy into your job will offer you with rewarding paychecks.

Tips about Career:

You must always have a career plan. Your career plan must move in an upward direction.

Your career would involve not just to get the tasks done, but also to gain experiences, learn novel skills, develop networks, and gain knowledge.

Tips about Profession:

Your profession is the benchmark for your job and career.

Make sure you select a wise profession. This will ensure that you land a promising job and have a positive career graph.

What Is The Difference Between Effort And Attempt?

Noun

()

The work involved in performing an activity; exertion.

* , chapter=23

, title= The Mirror and the Lamp , passage=The slightest effort made the patient cough. He would stand leaning on a stick and holding a hand to his side, and when the paroxysm had passed it left him shaking.}}

* {{quote-news, year=2011, date=June 22, author=Press Association, work=The Guardian

, title= Manchester United offer Park Ji-sung a new two-year contract , passage=The 30-year-old South Korean, who joined United in 2005, retired from international duty after last season’s Asian Cup in an effort to prolong his club}}

* {{quote-magazine, year=2013, month=July-August, author=(Henry Petroski)

, title=

* {{quote-magazine, date=2012-03, author=William E. Carter, Merri Sue Carter

, volume=100, issue=2, page=87, magazine=( American Scientist) , title= The British Longitude Act Reconsidered , passage=But was it responsible governance to pass the Longitude Act without other efforts to protect British seamen? Or might it have been subterfuge-a disingenuous attempt to shift attention away from the realities of their life at sea.}}

A force acting on a body in the direction of its motion.

Usage notes

* Adjectives often used with “effort”: conscious, good, poor, etc.

Derived terms

* best efforts * centre of effort * effort distance * effortless * make an effort

Verb

()

To try.

I attempted to sing, but my throat was too hoarse.

* Longfellow

Something attempted , something done, / Has earned a night’s repose.

* {{quote-magazine, year=2013, month=July-August, author= Sarah Glaz

, title= Ode to Prime Numbers , volume=101, issue=4, magazine=( American Scientist) , passage=Some poems, echoing the purpose of early poetic treatises on scientific principles, attempt to elucidate the mathematical concepts that underlie prime numbers. Others play with primes’ cultural associations. Still others derive their structure from mathematical patterns involving primes.}}

(obsolete) To try to move, by entreaty, by afflictions, or by temptations; to tempt.

* Thackeray

It made the laughter of an afternoon / That Vivien should attempt the blameless king.

(archaic) To try to win, subdue, or overcome.

one who attempts the virtue of a woman

* Shakespeare

Dear sir, of force I must attempt you further: / Take some remembrance of us, as a tribute.

(archaic) To attack; to make an effort or attack upon; to try to take by force.

* Motley

Usage notes

* This is a catenative verb that takes the to infinitive . See

Synonyms

* take a stab at, take a run at

Noun

()

The action of trying at something.

* We made an attempt to cross the stream, but didn’t manage.

* This poem is much better than the feeble attempt of mine.

* It was worth the attempt .

* {{quote-magazine, date=2012-03

, author=William E. Carter, Merri Sue Carter , title=The British Longitude Act Reconsidered , volume=100, issue=2, page=87 , magazine= citation , passage=But was it responsible governance to pass the Longitude Act without other efforts to protect British seamen? Or might it have been subterfuge-a disingenuous attempt to shift attention away from the realities of their life at sea}}

An assault or attack, especially an assassination attempt.

* 1584‘ ”No man can charge us of any ”’attempt against the realm. (Allen’s Defence Of English Catholics, cited after Edinburgh review 1883, p. 378)

Usage notes

* Adjectives often applied to “attempt”: first, failed, desperate, last, half-hearted, unsuccessful, serious, successful, feeble, new, honest, vain, sincere, ambitious, earnest, clumsy, direct, hard, brilliant, official, useless, clever, sophisticated, amateurish.

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