Error message in typecasting and dereferencing in c++!

Question

1.00/5 (1 vote)

See more:

I would like to ask how is it possible to do typecasting and then dereferencing in C++, I mean with C++ code not C. Here, it is a part of code which simply type casted in C, how can do that in C++?

C#

bool equals_double(const void* elem1, const void* elem2){
    if (*(int*)elem1 == *(int*)elem2)

I used this code in C++ but it doesn't work:

C#

bool equals_int(const void* elem1, const void* elem2){
    if (*(static_cast<int*>(elem1)) == *(static_cast<int*>(elem2))){
        return true;
    }
    else{
        return false;
    }
}

the error is:

C++

error: static_cast from type 'const void*' to type 'int*' casts away qualifiers|

Posted 17-Oct-15 10:06am

amin.j

Updated 17-Oct-15 20:50pm

v5

Add a Solution

Comments

Andreas Gieriet 17-Oct-15 17:46pm

What does your textbook tell about casting in C++?
Regards
Andi

Philippe Mori 17-Oct-15 17:51pm

You avoid unneccessy casting. You fonction should peobably tke doubles.... If you need casting, better to use C++ style cast list static_cast and others...

amin.j 18-Oct-15 0:54am

I did this code for substituting the typecasting in C++ instead of the above code in C but it doesn't work. There should be a dereferencing after typy casting.

bool equals_int(const void* elem1, const void* elem2){
if (*(static_cast<int*>(elem1)) == *(static_cast<int*>(elem2))){
....

Andreas Gieriet 18-Oct-15 2:43am

The error tells it all: "...qualifiers...": you cannot cast away constness with the static_cast operator - use ...<const int*>...
Regards
Andi
PS: Why do you change from double to int?

amin.j 18-Oct-15 2:49am

Dear Andreas, thanks a lot it works. However, is it possible to explain it more what is the error is about and what the solution does!

Andreas Gieriet 18-Oct-15 3:54am

Please do yourself and us the favor and read the documentation on the four C++ cast operators yourself.
Regards
Andi

amin.j 18-Oct-15 3:02am

How can do the same for Class data type, here DayOfear:

bool equals_class(const void* elem1, const void* elem2){
`if ((*(DayOfYear*)elem1).month == (*(DayOfYear*)elem2).month && (*(DayOfYear*)elem1).day == (*(DayOfYear*)elem2).day){`

I use this one:
`if ((*(static_cast<dayofyear*>(elem1)).month == (*(static_cast<dayofyear*>(elem2)).monthh &&
(*(static_cast<dayofyear*>(elem1)).day == (*(static_cast<dayofyear*>(elem2)).day){`

but it makes error:
static_cast from type 'const void*' to type 'DayOfYear*' casts away qualifiers|

Richard MacCutchan 18-Oct-15 3:30am

You should use const_cast since you are casting away the constness of the variables. As it clearly tells you in the error message.

amin.j 18-Oct-15 3:44am

This code is working:
if(*(static_cast<const int*="">(elem1)) == *(static_cast<const int*="">(elem2)))

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Andreas Gieriet · Answer 1 · 2015-10-17T11:47:00

Solution 1

How about Google?
E.g. see http://www.cplusplus.com/doc/tutorial/typecasting/[^].
Regards
Andi

Posted 17-Oct-15 11:47am

Andreas Gieriet

Comments

[no name] 18-Oct-15 12:11pm

A 5.

Andreas Gieriet 18-Oct-15 13:42pm

Thanks for your 5!
Cheers
Andi