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Is it good useful meaningful worthwhile to use register variables in C++?
The register keyword has been largely ignored by compilers for decades. In C, it prevents you from taking the address of a variable. But otherwise, most compilers ignore the hint it offers.
STANDARD C++ does not support register variables in 2022. In C register variables serve as a hint to the compiler to use a register rather than a memory address. Prior to C++17, it could also be used as a hint to the compiler in C++ as well, but only some conforming compilers did anything as a result. Starting in C++17, register has become an unused but reserved keyword.
Some compilers still permit it and some may even honor the request. Your programs, however, will not be cross-platform or written in true, standards-compliant C++ if you use the register keyword.
NOTE:
The situation in C (as opposed to C++) is quite different.
“Is it good?”
Usually the answer to that question is that it’s the wrong question, and that you should instead ask “Is it useful/meaningful/worthwhile…?” For example, if you had asked about using the register keyword in C, I would say “There’s nothing wrong about it. It won’t harm your program. It’s just a waste of time.”
It turns out C++ deprecated the register keyword in C++11, and removed it in C++17. As of C++17, the keyword register is now a reserved word with no meaning.
So, the answer to “is it good?” is “No.” Your program will fail to compile as a C++17 program.
By the end of 90s, register was the “R-type” decal of the C programming world. It did about as much for the speed of your program as the decal did for your car. (Possible exception for weak compilers on some embedded platforms.)
In any case, it doesn’t make sense to have a register qualifier on a parameter in a function prototype. It is ignored on any function declaration that is not a definition, similar to top level const.
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That is, all four of these are equivalent:
- void foo(int x);
- void foo(const int x);
- void foo(register int x);
- void foo(register const int x);
Now, both of those are meaningful in a definition. The register keyword stops you from taking an address (in C, but not C++), and const stops you from mutating the variable.
- void foo(register const int x) {
- const int *px = &x; // ERROR
- x = 42; // ERROR
- }
So, in principle you should be able to delete the unnecessary and useless register keywords from.the prototypes in the header without affecting any aspect of the program’s speed or correctness.
As of C++17 the use of the register qualifier has been removed. It’s now an unused reserved word.
Old? It is outright obsolete and even if you’re coding on an older version you’re advised to not use it for forward compatibility.
It was a hint to the compiler that a variable would be frequently accessed and the the compiler should prefer to use a CPU register to hold it. The downside being you can’t take the address of a register.
In days of yore (pre-millennium) on now arcane and primitive architectures significant improvements could be had from making (typically) the control variable of a for-loop as a register.
I’m sure that’s still true of some embedded platforms. But modern CPUs have multiple tiers of memory cache and the overhead of loading from and storing variables to main memory is less significant.
We no longer really live with the simplistic Von Neumann of CPU and Main Memory with nothing in between.
Also, optimizers have vastly improved and will tend to make good choices for storage on their own.
It was removed from the standard not because its use was doing harm but that it was regarded as having little practical value and the keyword may be useful in the future.
Reference: here
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List of Freely available programming books - What is the single most influential book every Programmers should read
- Bjarne Stroustrup - The C++ Programming Language
- Brian W. Kernighan, Rob Pike - The Practice of Programming
- Donald Knuth - The Art of Computer Programming
- Ellen Ullman - Close to the Machine
- Ellis Horowitz - Fundamentals of Computer Algorithms
- Eric Raymond - The Art of Unix Programming
- Gerald M. Weinberg - The Psychology of Computer Programming
- James Gosling - The Java Programming Language
- Joel Spolsky - The Best Software Writing I
- Keith Curtis - After the Software Wars
- Richard M. Stallman - Free Software, Free Society
- Richard P. Gabriel - Patterns of Software
- Richard P. Gabriel - Innovation Happens Elsewhere
- Code Complete (2nd edition) by Steve McConnell
- The Pragmatic Programmer
- Structure and Interpretation of Computer Programs
- The C Programming Language by Kernighan and Ritchie
- Introduction to Algorithms by Cormen, Leiserson, Rivest & Stein
- Design Patterns by the Gang of Four
- Refactoring: Improving the Design of Existing Code
- The Mythical Man Month
- The Art of Computer Programming by Donald Knuth
- Compilers: Principles, Techniques and Tools by Alfred V. Aho, Ravi Sethi and Jeffrey D. Ullman
- Gödel, Escher, Bach by Douglas Hofstadter
- Clean Code: A Handbook of Agile Software Craftsmanship by Robert C. Martin
- Effective C++
- More Effective C++
- CODE by Charles Petzold
- Programming Pearls by Jon Bentley
- Working Effectively with Legacy Code by Michael C. Feathers
- Peopleware by Demarco and Lister
- Coders at Work by Peter Seibel
- Surely You're Joking, Mr. Feynman!
- Effective Java 2nd edition
- Patterns of Enterprise Application Architecture by Martin Fowler
- The Little Schemer
- The Seasoned Schemer
- Why's (Poignant) Guide to Ruby
- The Inmates Are Running The Asylum: Why High Tech Products Drive Us Crazy and How to Restore the Sanity
- The Art of Unix Programming
- Test-Driven Development: By Example by Kent Beck
- Practices of an Agile Developer
- Don't Make Me Think
- Agile Software Development, Principles, Patterns, and Practices by Robert C. Martin
- Domain Driven Designs by Eric Evans
- The Design of Everyday Things by Donald Norman
- Modern C++ Design by Andrei Alexandrescu
- Best Software Writing I by Joel Spolsky
- The Practice of Programming by Kernighan and Pike
- Pragmatic Thinking and Learning: Refactor Your Wetware by Andy Hunt
- Software Estimation: Demystifying the Black Art by Steve McConnel
- The Passionate Programmer (My Job Went To India) by Chad Fowler
- Hackers: Heroes of the Computer Revolution
- Algorithms + Data Structures = Programs
- Writing Solid Code
- JavaScript - The Good Parts
- Getting Real by 37 Signals
- Foundations of Programming by Karl Seguin
- Computer Graphics: Principles and Practice in C (2nd Edition)
- Thinking in Java by Bruce Eckel
- The Elements of Computing Systems
- Refactoring to Patterns by Joshua Kerievsky
- Modern Operating Systems by Andrew S. Tanenbaum
- The Annotated Turing
- Things That Make Us Smart by Donald Norman
- The Timeless Way of Building by Christopher Alexander
- The Deadline: A Novel About Project Management by Tom DeMarco
- The C++ Programming Language (3rd edition) by Stroustrup
- Patterns of Enterprise Application Architecture
- Computer Systems - A Programmer's Perspective
- Agile Principles, Patterns, and Practices in C# by Robert C. Martin
- Growing Object-Oriented Software, Guided by Tests
- Framework Design Guidelines by Brad Abrams
- Object Thinking by Dr. David West
- Advanced Programming in the UNIX Environment by W. Richard Stevens
- Hackers and Painters: Big Ideas from the Computer Age
- The Soul of a New Machine by Tracy Kidder
- CLR via C# by Jeffrey Richter
- The Timeless Way of Building by Christopher Alexander
- Design Patterns in C# by Steve Metsker
- Alice in Wonderland by Lewis Carol
- Zen and the Art of Motorcycle Maintenance by Robert M. Pirsig
- About Face - The Essentials of Interaction Design
- Here Comes Everybody: The Power of Organizing Without Organizations by Clay Shirky
- The Tao of Programming
- Computational Beauty of Nature
- Writing Solid Code by Steve Maguire
- Philip and Alex's Guide to Web Publishing
- Object-Oriented Analysis and Design with Applications by Grady Booch
- Effective Java by Joshua Bloch
- Computability by N. J. Cutland
- Masterminds of Programming
- The Tao Te Ching
- The Productive Programmer
- The Art of Deception by Kevin Mitnick
- The Career Programmer: Guerilla Tactics for an Imperfect World by Christopher Duncan
- Paradigms of Artificial Intelligence Programming: Case studies in Common Lisp
- Masters of Doom
- Pragmatic Unit Testing in C# with NUnit by Andy Hunt and Dave Thomas with Matt Hargett
- How To Solve It by George Polya
- The Alchemist by Paulo Coelho
- Smalltalk-80: The Language and its Implementation
- Writing Secure Code (2nd Edition) by Michael Howard
- Introduction to Functional Programming by Philip Wadler and Richard Bird
- No Bugs! by David Thielen
- Rework by Jason Freid and DHH
- JUnit in Action
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