DaniWeb Forum Index > Software Development > C++

Urgent :decrement of read-only location

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Sep 2009

Posts: 16

Reputation: aomran is an unknown quantity at this point

Solved Threads: 0

aomran

Offline

Newbie Poster

Urgent :decrement of read-only location

Sep 23rd, 2009

Hi everyone,

Can anyone tells me what this error means:

error: decrement of read-only location.

thanks

•

Join Date: Apr 2004

Posts: 4,452

Reputation: Dave Sinkula has a brilliant future

Solved Threads: 250

Dave Sinkula Dave Sinkula is offline

Offline

long time no c

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

My guess is that it means just what it says.

Do you suppose you could post relevant code or some sort of context?

"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand

•

Join Date: Sep 2009

Posts: 16

Reputation: aomran is an unknown quantity at this point

Solved Threads: 0

aomran

Offline

Newbie Poster

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

I will post the relevant code shortly, but I need more explanation of what decrement of read only location. location of what and how it has been decremented.

•

Join Date: Nov 2008

Posts: 397

Reputation: StuXYZ is a glorious beacon of light

Solved Threads: 72

StuXYZ

Offline

Posting Whiz

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

well your compile should give a line number.....
What you are not saying is if the error is at run-time or at compile time.

Compile time:

you may have written something like this

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
const int X(40);       // set X to 40
X--;                          // set X to 39 not allowed.
const int X(40);       // set X to 40
X--;                          // set X to 39 not allowed.

Run time, you may have written:

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
int *Ptr(10);   // intending *Ptr to point to a location 10  but 
                      // actually pointing it to location 
// error here:
(*Ptr)--;         // Maybe you intended to write *Ptr--
int *Ptr(10);   // intending *Ptr to point to a location 10  but 
                      // actually pointing it to location 
// error here:
(*Ptr)--;         // Maybe you intended to write *Ptr--

Actually the last error is a little difficult to find, without using the debugger or a lot of print statements.

experience is the most expensive way to learn anything

•

Join Date: Jun 2009

Posts: 194

Reputation: necrolin will become famous soon enough

Solved Threads: 19

necrolin

Offline

Junior Poster

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

Like the others already stated this error comes from trying to manipulate a constant. This should make you wonder a few things including:

Why am I trying to manipulate a constant? It totally beats the point of making something constant if you're going to decrement it later.

If you have to decrement the constant then why not just remove the const and make it a normal variable?

However, if you really need to do this and there's some logical reason for it then there's always const_cast<>. Take a look at my example:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main()
{
   const int myVar = 5;
   int* j = const_cast<int*>(&myVar);
   *j = *j - 1;
   cout << *j << ": as you can see it's been decremented to 4.\n";
 
   return 0;
}
int main()
{
   const int myVar = 5;
   int* j = const_cast<int*>(&myVar);
   *j = *j - 1;
   cout << *j << ": as you can see it's been decremented to 4.\n";

   return 0;
}

•

Join Date: Dec 2007

Posts: 360

Reputation: jencas is just really nice

Solved Threads: 69

jencas

Offline

Posting Whiz

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

Or maybe you have a const method and you try to decrement a member variable in this method.

Last edited by jencas; Sep 23rd, 2009 at 5:13 am.

If you are forced to reinvent the wheel at least try to invent a better one!

Please use code tags - Please mark solved threads as solved

•

Join Date: Sep 2009

Posts: 16

Reputation: aomran is an unknown quantity at this point

Solved Threads: 0

aomran

Offline

Newbie Poster

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

I actually got these two messages

dheap.h: In member function ‘void Dheap<Process>::deleteMin() const’:
dheap.h:191: error: decrement of read-only location

•

Join Date: Jun 2009

Posts: 194

Reputation: necrolin will become famous soon enough

Solved Threads: 19

necrolin

Offline

Junior Poster

Re: Urgent :decrement of read-only location

Sep 23rd, 2009

The "const" at the end of your first error line is your problem. The member function is declared constant so it won't allow you to make any changes to variables in the function.