Thread: deprecated conversion from string constant to char*

Where exactly do you get that warning?

that line doesn't appear to be the problem. you'll usually get that warning when you do something like this:

Code:

char* myString = "foo!";

Originally Posted by baxy

ok, so i'm lost, why did this work?

Code:

function( const_cast < char* > ( args.i.c_str() ) );

Because function is not const-correct (assuming it does not modify the data pointed at by its argument).

args.i.c_str() returns a pointer to a CONSTANT string (const char *) while your function is expecting a non-constant string (char *). Your cast is explicitly telling the compiler it's OK to pass a pointer to a constant in this instance.

The better method would have been to code function() to take a parameter that is of type const char *, assuming it couldn't be modified to take a string.

Again, this is all assuming that function() does not modify the string. If it does, then additional work is needed.

Well, this doesn't make any sense: the type of the argument to the function named function in post #1 in both cases is the same as the type of the argument after the const_cast to char* is applied. Hence, I do not see why the warning should disappear, unless you removed some other offending code that you have not shown us.

As has been mentioned, the use of const_cast will be correct if the function's parameter is not const correct. If it does modify what the pointer points to, then you have undefined behaviour instead, in which case it might appear to work, but actually doesn't.

Originally Posted by laserlight

If it does modify what the pointer points to, then you have undefined behaviour instead, in which case it might appear to work, but actually doesn't.

Technically, a permitted result of undefined behaviour is that code which appears to work actually does. The problem is, that code is not guaranteed to work, and is permitted to work incorrectly, can work with one compiler but not another, etc etc.