Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

error e2093: how to avoid it?

Posted on 2001-06-09
5
Medium Priority
?
373 Views
Last Modified: 2007-12-19
hello,
i hope some of you are c++ gurus and can help me:

long time ago i've written my own vector class:

class cls_vector
{
     ...
     cls_vector mth_sum(cls_vector &rfr_vector_2);
     cls_vector operator+(cls_vector &rfr_vector_2);
     ...
};

(both methods do exactly the same)

now i wanted to compile a simple test program with the borland c++ compiler (bcc32):

//works fine!
a.mth_sum(b+a); //a and b are both vector objects

//causes e2093
a+(b+a);

and now i get the following error message:
"e2093 operator '+' not implemented in type 'cls_vector' for arguments of the same type"!

i really don't know what the reason for this error is because i compiled these expressions with turbo c++ without any errors!
and i don't see any difference between these expressions but it still doesn't work!

please help me!
thanks, 239
0
Comment
Question by:ef239
  • 4
5 Comments
 
LVL 22

Accepted Solution

by:
nietod earned 200 total points
ID: 6171795
The problem is that your classes are not const correct (contant correct).

in code like

a+(b+c)

the b+c is performed first and this creates an unnamed temporary object, then this unamed temporary object is added to a.  As if you did

cls_vector temp = b+c;
a + temp;

the problem is that unnamed temporaries nmust be treated like constant objects.  but your functions are declared to take non-constant parameters.  This makes sense.  Why woudl you want to change a temproary value that you never "see".  If the functions really do alter their parameters, then you must leave them this way and you may not use the function as you trying to do so.  But that is unlikely.  so most likely you shoiuld follow the standard convention passing constant parmaters do the binary mathematical operators.


0
 
LVL 22

Expert Comment

by:nietod
ID: 6171799
for example,

cls_vector mth_sum(const cls_vector &rfr_vector_2) const
cls_vector operator+(const cls_vector &rfr_vector_2) const;
                 ...
this decalres both the named parameter and the "this" parameter as constants.

Note however, that it is usually a bette idea to declare operator + as a free function, not as a member function.  Among other reasons this will allow automatic conversions to be applied to both the left and right operands.  if the operator is a meber function, then the conversios will be aplied to only the right operand.  fior example

cls_vector operator+(const cls_vector &rfr_vector_1,const cls_vector &rfr_vector_2)
{
   return vactor_1.mth_sum(vector_2);
}
0
 
LVL 22

Expert Comment

by:nietod
ID: 6171801
>>  i compiled these expressions with turbo
>> c++ without any errors!
turbo C++ was abandoned 7+ years before the C+ standard was completed.  Its about as current as gas lamps and horse-drawn carriages.
0
 
LVL 22

Expert Comment

by:nietod
ID: 6171824
>> //works fine!
>> a.mth_sum(b+a); //a and b are both vector objects
Technically this should not compile either.  If it does, your compiler is at fault.  If you are using an outdated compiler like one of the free copies of BCB you might find that code like this still compiles, evne though it shouldn't.  Your best bet is to modernize.
0
 

Author Comment

by:ef239
ID: 6173488
ok, thanks for your help!
(i compiled it with borland free command line tools 5.5)
0

Featured Post

What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
Article by: evilrix
Looking for a way to avoid searching through large data sets for data that doesn't exist? A Bloom Filter might be what you need. This data structure is a probabilistic filter that allows you to avoid unnecessary searches when you know the data defin…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
Suggested Courses

916 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question