/* Example Utility This example takes advantage of some important stream facilities Writes out logfile entries from command line arguments http://www.cprogramming.com/tutorial/c++-iostreams.html */ #ifdef _MSC_VER #define _CRT_SECURE_NO_WARNINGS #endif #include #include #include #include //time stamp returns the current time as string std::string timestamp(); class LogStatement; std::ostream& operator<<(std::ostream& ost, const LogStatement& ls); class LogStatement { public: LogStatement(std::string s) : data(s), time_string(timestamp()) { }; //this method handles all the outputs friend std::ostream& operator<<(std::ostream&, const LogStatement&); private: std::string data; std::string time_string; }; std::ostream& operator<<(std::ostream& ost, const LogStatement& ls) { ost << "~| " << ls.time_string << " | " << ls.data << "|~"; return ost; } std::string timestamp() { //notice the use of a string stream, yet another useful stream medium std::ostringstream stream; time_t rawtime; tm * timeinfo; // get current calender time as a value of type time_t - see: http://www.cplusplus.com/reference/ctime/time/ std::time(&rawtime); //convert time_t to tm as local time time - see: http://www.cplusplus.com/reference/ctime/localtime/ timeinfo = std::localtime(&rawtime); //create stream that we will use to output std::string: see: http://www.cplusplus.com/reference/sstream/ostringstream/ stream << (timeinfo->tm_year) + 1900 << "/" << timeinfo->tm_mon << "/" << timeinfo->tm_mday << " " << timeinfo->tm_hour << ":" << timeinfo->tm_min << ":" << timeinfo->tm_sec; //the str() function of output stringstreams returns a std::string return stream.str(); } int main(int argc, char** argv) { if (argc < 2) { // a return on -1 denotes an error condition return -1; } std::ostringstream log_data; //take all the char arrays in argv (except filename) and produce a stream for (int i = 1; i < argc; i++) { log_data << argv[i] << " "; } LogStatement log_entry(log_data.str()); // clog - Standard output stream for logging - see: http://www.cplusplus.com/reference/iostream/clog/ also see: http://en.cppreference.com/w/cpp/io/clog std::clog << log_entry << std::endl; // ofstream : Output stream class to operate on files - see: http://www.cplusplus.com/reference/fstream/ofstream/ std::ofstream logfile("logfile", std::ios::app); //check for errors opening the file if (!logfile) { //could not open file - return error return -1; } // output stream to file logfile << log_entry << std::endl; //close file logfile.close(); // exit success return 0; }

stream - example