Is it safe to pass std::string to C style APIs?

Question

It is well defined C++ to pass std::vector to C APIs that expect an output array like so because std::vector is contiguous:

std::vector myArray(a         


        

Answer 1

If the C API function requires read-only access to the contents of the std::string then use the std::string::c_str() member function to pass the string. This is guaranteed to be a null terminated string.

If you intend to use the std::string as an out parameter, C++03 doesn't guarantee that the stored string is contiguous in memory, but C++11 does. With the latter it is OK to modify the string via operator[] as long as you don't modify the terminating NULL character.