advertisement
Premier Club Log In/Registration
  Include Code  Search Tips
TODAY'S HEADLINES  |   ARTICLE ARCHIVE  |   SKILLBUILDING  |   TIP BANK  |   SOURCEBANK  |   FORUMS  |   NEWSLETTERS
Browse DevX
Partners & Affiliates
advertisement
advertisement
Tip of the Day
Average Rating: 4/5 | Rate this item | 1 user has rated this item.
Expertise: All
Language: C++
April 30, 1999
What are Lvalues and Rvalues?
An object is a contiguous region of memory storage. An lvalue (pronounced: L value) is an expression that refers to such an object. The original definition of lvalue referred to "an object that can appear on the left-hand side of an assignment." However, const objects are lvalues, and yet they cannot appear on the left-hand side of an assignment. An expression that can appear in the right-hand side of an expression (but not in the left-hand side of an expression) is an rvalue. For example:
 
#include <string>
using namespace std;
int& f();

void func()
{
  int n;
  char buf[3]; 
  n = 5;   // n is an lvalue; 5 is an rvalue
  buf[0] = 'a';   //buf[0] is an lvalue, 'a' is an rvalue
  string s1 = "a", s2 = "b", s3 = "c";  // "a", "b", "c" are rvalues
  s1 =  // lvalue
      s2 +s3;   //s2 and s3 are lvalues that are implicitly converted to rvalues
  s1 =  
      string("z");    // temporaries are rvalues
  int * p = new int;    // p is an lvalue; 'new int' is an rvalue
  f() = 0;    // a function call that returns a reference is an lvalue
  s1.size();   // otherwise, a function call is an rvalue expression
}
An lvalue can appear in a context that requires an rvalue; in this case, the lvalue is implicitly converted to an rvalue. An rvalue cannot be converted to an lvalue. Therefore, it is possible to use every lvalue expression in the example as an rvalue, but not vice versa.
Danny Kalev
If you have a hot tip and we publish it, we'll pay you. However, due to accounting overhead we no longer pay $10 for a single tip submission. You must accumulate 10 acceptable tips to receive payment. Be sure to include a clear explanation of what the technique does and why it's useful. If it includes code, limit it to 20 lines if possible. Submit your tip here.
advertisement
Untitled
advertisement
Advertising Info  |   Member Services  |   Permissions  |   Contact Us  |   Help  |   Feedback  |   Site Map  |   Network Map  |   About


JupiterOnlineMedia

internet.comearthweb.comDevx.commediabistro.comGraphics.com

Search:

Jupitermedia Corporation has two divisions: Jupiterimages and JupiterOnlineMedia

Jupitermedia Corporate Info


Legal Notices, Licensing, Reprints, & Permissions, Privacy Policy.

Advertise | Newsletters | Tech Jobs | Shopping | E-mail Offers

Solutions
Whitepapers and eBooks
Intel PDF: Virtualization Delivers Data Center Efficiency
Intel eBook: Managing the Evolving Data Center
Microsoft Article: BitLocker Brings Encryption to Windows Server 2008
Symantec eBook: The Guide to E-Mail Archiving and Management
Microsoft Article: RODCs Transform Branch Office Security
Go Parallel Article: James Reinders on the Intel Parallel Studio Beta Program
Avaya Article: Advancing the State of the Art in Customer Service
Adobe Acrobat Connect Pro: Web Conferencing and eLearning Whitepapers
Avaya Article: Avaya AE Services Provide Rapid Telephony Integration with Facebook
Go Parallel Article: Getting Started with TBB on Windows
HP eBook: Storage Networking , Part 1
MORE WHITEPAPERS, EBOOKS, AND ARTICLES
Webcasts
Intel Seminar: Efficiencies in Hardware/Software Virtualization
HP Webcast: Disaster Recovery Planning
Go Parallel Video: Performance and Threading Tools for Game Developers
HP Video: StorageWorks EVA4400 and Oracle
HP Webcast: Storage Is Changing Fast - Be Ready or Be Left Behind
MORE WEBCASTS, PODCASTS, AND VIDEOS
Downloads and eKits
IBM TCO eKIT: Your IT Budget is Under Attack, Get in Control
IBM Energy Efficiency eKIT: Learn How to Reduce Costs
30-Day Trial: SPAMfighter Exchange Module
Red Gate Download: SQL Toolbelt and free High-Performance SQL Code eBook
Iron Speed Designer Application Generator
MORE DOWNLOADS, EKITS, AND FREE TRIALS
Tutorials and Demos
Microsoft Article: Silverlight Streaming--Free Video Hosting for All
Featured Algorithm: Intel Threading Building Blocks - parallel_reduce
HP Demo: StorageWorks EVA4400
MORE TUTORIALS, DEMOS AND STEP-BY-STEP GUIDES