There are two constructors, one where the filename and open mode are of type std::string, the other where the types are const char*. Permitted open modes are:
| Mode | Description |
| r | read |
| w | write |
| a | append |
| u | synonym for append |
cyclic_log(const std::string& filename, const std::string& openMode); cyclic_log(const char* filename, const char* openMode);Open logfile for read, write or append. Any file system error encountered during the opening of the file is handled by an exception of type std::runtime_error being thrown. The exception is a complete report of what exactly went wrong.