Is it better to use c_str or toCharArray?

Question

When reading/trying a recent answer, I was surprised to see that Arduino's String class supports the c_str() method, just like the C++ std::string class. As expected, it appears to get a pointer to the string's contents as a null-terminated char array (i.e. C-style string).

However, (as far as I can see) that method is not mentioned in the official Arduino documentation. Additionally, in all example code I've seen using String, a different approach seems to be used. A secondary char buffer is setup, and then the contents of the string are copied to it using String::toCharArray(). This obviously requires double the memory, plus an O(n) copy operation.

It seems like c_str() should be the preferred approach. Is there some reason why toCharArray() is more commonly used?

Answer 1

It seems like c_str() should be the preferred approach. Is there some reason why toCharArray() is more commonly used?

basically, I'd say it's a lack of knowledge from the people doing the codes you've seen. Definitely c_str() is better. Though, what I see even more often is the use of character arrays char* strings instead of String (and I plead guilty of that as well in my own codes).

And that's because the Arduino library has been built upon a messy set of C and C++ libraries and coding style. Trying to make things easier actually messed them up and complicated them more.

That's actually why we have new projects like xpcc trying to make a real and smart use of the C++ abilities in the embedded world.