RE: [Dev-C++] const modifier?

[Ioannis V. <no...@ho...>]

> -----Original Message-----
> From: dev...@li... 
> [mailto:dev...@li...] On Behalf 
> Of Abhijit Shylanath
> Sent: Friday, June 14, 2002 8:13 PM
> To: Dev-C++ Mailing List
> Subject: [Dev-C++] const modifier?
> 
> 
> I was just going through the sources of the class libraries 
> in Turbo C++
> version 3.0, and found this code. How does the program modify 
> aPtr even
> though it says it's a const?


const char *p means that it can not change the contents of the object
where it points. Example:


const char *p="constast string 1";
p="constant string 2";


To not be able to point to somewhere else:

// constant pointer
char * const p=some_char_array;


const char *const p="something";


p cannot point to somewhere else and cannot changge the object where it
points. For example:

cout<<p[2]; // valid

p[2]='7'; // invalid

p="something else"; //invalid

for(int i=0; i<18; i++)
cout<<"did you know that?"[i]; // valid

> 
> -------CLASSLIB/SOURCE/STRNG.CPP------
> String::String( const char *aPtr )
> {
>     if ( aPtr == 0 )
>         aPtr = "";
> 
>     len = strlen( aPtr ) + 1;
>     theString = new char[ len ];
>     CHECK( theString != 0 );
>     strcpy( theString, aPtr );
> }
> --------------------------------------
> 
> After seeing this, I tried compiling the following file in 
> MingW, and it did
> (with -Wall, no warnings)
> 
> --------------------------------------
> void  do_stuff(const char *buf)
> {
>   if(!buf)
>     buf = "";
> }
> 
> int main()
> {
>   do_stuff(0);
>   return 0;
> }
> --------------------------------------
> 
> How? Doesn't
>     buf = "";
> translate to assign "" to buf?


A literal behaves like an array of chars. An array behaves like a
pointer to its first element. The first element here is '\0' (which is
always 0). I did not understand the last question btw.


Since you learn C++ i recommend you leave the low level  stuff for
later, and learn to deal C++ as a high level language, and not as C.



Ioannis

* Ioannis Vranos
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