Can c++ strings be used as char buf[]?

I'm playing around with some sockets and most of the c based commands utilise char buf[BUFSIZE]. I've been using c++ strings and sending &string[0] whenever a char * is required. I'm aware that a buf can be a string or not depending on wether is is null terminated but is it a bad idea to force a c++ string object into a char buf[]?

why dont u just convert it out of the C++ string to a C string?

It is a bad idea only if the function alters the char buffer. This is because, the string object may keep the size of the string allocated in a different member of the class (depending on the implementation of course), and if the function alters the char buffer, interesting things might occur later on. If the function accepts a const char* instead of a char *, then at least you have some assurance that the function is not going to alter the contents. BTW string objects have a c_str() member function which returns the pointer to the char array of the object.