why i can't compile this in visual c++ 6

[jianmin jin]

#include <cstring>

class Text
{
public:
void bad( const string &parm ) const;
private:
char *_text;
};
void Text::bad( const string &parm ) const
{
_text = parm.c_str();
for( int ix = 0; ix < parm.size(); ++ix )
_text[ix] = parm[ix];
}
int main( int argc, char **argv)
{
return 0;
}

[rxbagain]

#include <string>
using namespace std;

Hope this will help you

[jianmin jin]

Originally posted by rxbagain

#include <string>
using namespace std;

Hope this will help you

thanks a lot

[Paul McKenzie]

Originally posted by jianmin jin
void Text::bad( const string &parm ) const
{
_text = parm.c_str();
for( int ix = 0; ix < parm.size(); ++ix )
_text[ix] = parm[ix];
}

jianmin jin,

I hope you called this function "bad", because it is bad.

The code you have here will invoke undefined behavior and is flawed. The problem is that c_str() returns a const char *. This means that you are not allowed to change characters. Your loop changes _text which is pointing to a const char *. Your code may crash, it may work, you don't know.

Regards,

Paul McKenzie

[Graham]

The compiler should cough at the line:

_text = parm.c_str();

since the assignment loses cv-qualifiers.

Also, can I once again point out that leading underscores in names are reserved by the standard for use by compiler and standard library writers only:
Section 17.4.3.1.2:

— Each name that contains a double underscore (_ _) or begins with an underscore followed by an uppercase letter (2.11) is reserved to the implementation for any use.
— Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.