Question

If an input const string is being modified in some way (which is resulting in C compiler warning), what is the best way to handle it – typecasting it to a new variable and then using it OR duplicating it and using it and then freeing it. Or is there any other way to handle this type of scenario. please suggest. Any help would be appreciated.

//Typecasting

const char * s1;
char * s2 = (char *)s1;

//Duplicate and free

const char * s1;
char * s2  = strdup( s1 );
free(s2)

EDIT: It is a C compiler; not C++. I am not sure whether in typecasting, s2 will be a new copy of string s1 or will it be pointing to the original string s1?

Thanks for the answers. I have one more doubt-

const char * c1;
const char * c2 = c1;

Is the above assignment valid?

Answer 1

Casting away const here might shut the compiler up but will lead to runtime failures. Make a copy of the string and work on that.

Casting away const does not copy the contents of the memory. It just creates a pointer to the same memory and tells the compiler that it can go right ahead and write to that memory. If the memory is read only you have a protection fault. More seriously you can have correctness problems which are hard to debug. Don’t cast away const.

Of course, if you need to modify a variable and have those modifications visible to the caller, then you should not make it const in the first place. On the other hand, if the modifications are meant to be private to the function, then duplication of the const parameter is best.

As a broad rule you should attempt to avoid casts if at all possible. Casts are one of the most frequent sources of errors.