Re: What's wrong with this?

[EMAIL PROTECTED] (Joe Developer) wrote
> This code crashes at run time with a memory fault on the assignment
> statement. I tried it under MSVC 6 and GC++. It worked in Borland C
> many years ago. Boy do I feel stupid.
> 
> void main()
> {
>         char *foo = "Hello World";
>         foo[0] = '9';  //crashes here.
> }

The string "Hello World" sets aside 12 bytes (including the null
byte) in a READ-ONLY section of memory. The data type of the string
is char*, but that's only because so much legacy code (especially
in C, as opposed to C++) expects it that way. The data type really
ought to be const char*, because you are not allowed to write into
it.

(By the way, if you had tried this in Borland C:
    for (i=0; i<2; ++i) {
        char *foo = "Gello World";
        ++*foo;
        cout<<foo<<endl;
    }
You would have gotten
    Hello World
    Iello World
because you're modifying the one-and-only copy of the string!)

Try this instead:
    char foo[] = "Hello World"; // This COPIES the 12 bytes
    foo[0] = '9'; // No problem now
You can do this as often as you need, because now you're only
modifying a copy.

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