You need to add a cast, since you're passing constant data to a function that says "I might change this":
send_str((char *) mystr); /* cast away the const */
Of course, if the function does decide to change the data that is in reality supposed to be constant (such as a string literal), you will get undefined behavior.
Perhaps I mis-understood you, though. If send_str()
never needs to change its input, but might get called with data that is non-constant in the caller's context, then you should just make the argument const
since that just say "I won't change this":
void send_str(const char *str);
This can safely be called with both constant and non-constant data:
char modifiable[32] = "hello";
const char *constant = "world";
send_str(modifiable); /* no warning */
send_str(constant); /* no warning */