15.16.7 write

oefpos_t write(const char          *buffer, oefpos_t len)
oefpos_t write(const signed char   *buffer, oefpos_t len)
oefpos_t write(const unsigned char *buffer, oefpos_t len)
oefpos_t write(const std::string   &buffer, oefpos_t len)

Writes len number of bytes from the specified data source (buffer) onto the output stream and returns the number of bytes that were able to be written.