• Jens Friese (20/20) Nov 30 2003 Hi,
• Cesar Rabak (15/42) Nov 30 2003 The "mystery" part can be solved by a good book on C and C++.

Jens Friese <Jens_member pathlink.com> writes:

Hi,

to my profound astonishment, this code works just fine: (same as attachment)

#include <iostream.h>

double data[41][41];

int main(int argc, char* argv[]){

data[40][1000]=3.4;    // <<<<< HOW CAN THIS BE???????

cout << data[40][1000];

}

The console output is: 3.4 !!!!!

What am I doing wrong? Shoulnd't data[40][40] be the outmost field of data?

I wonder if you can solve this mystery... 

Kind Regards

Jens


begin 0644 error.cpp




`
end

Cesar Rabak <csrabak ig.com.br> writes:

Jens Friese escreveu:
 Hi,
 
 to my profound astonishment, this code works just fine: (same as attachment)
 
 #include <iostream.h>
 
 double data[41][41];
 
 int main(int argc, char* argv[]){
 
 data[40][1000]=3.4;    // <<<<< HOW CAN THIS BE???????
 
 cout << data[40][1000];
 
 }
 
 The console output is: 3.4 !!!!!
 
 What am I doing wrong? Shoulnd't data[40][40] be the outmost field of data?
 
 I wonder if you can solve this mystery... 

The "mystery" part can be solved by a good book on C and C++.

The summary is that these languages are not 'memory managed' and the 
program you wrote fall under the 'undefined behaviour' the standards for 
them talk about.

One of these undefined consequences is the one you're seeing: 
_aparently_ it works but it carries a *bug* (if you've not coded it 
would be hidden, or worse, the program would exhibit erratic behaviour).

In order to check for these errors you'll need to use addon libraries 
like Electricfence, YAMD, etc.

HTH

 
 Kind Regards
 
 Jens
 
 



-- 
Cesar Rabak
GNU/Linux User 52247.
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