How can I change the values of the system clock using C++? - c++

Question

I've been trying to figure out how to use the system clock for a class project. The goal is to display the system's current time, then through inputs of 1-4 add one hour, minute, or second, then display the clock again. I think I have the basic framework down but I cannot figure out how to display the system time correctly as well as change the time itself. I have researched a few of the libraries to use and it gets pretty confusing with the pointers and the way it also always prints the date as well. I'm still new to C++ so my code is not the best especially when formatting the functions for the displays. Any help is appreciated.
When I run the program I want to print the local time from the PC it is running on, then receive input from the user (keystroke 1 - 4), then print the new time again. I don't want to actually change the time on my PC. For example say the current local time of my computer is 08:22:14, which will print to the screen. I wait any amount of time before I input selection 2. The new time will print 08:23:14.
#define _CRT_SECURE_NO_WARNINGS
#include <time.h> /* time_t, struct tm, time, localtime */
#include <iostream> // std::cout, std::endl
#include <iomanip> // std::setfill, std::setw
#include <stdlib.h> // system(CLS);
#include <Windows.h>
#include <ctime>
using namespace std;
int DisplayClocks(int time) { // Function to write both clocks to screen
std::cout << std::setfill('*') << std::setw(26) << " " << std::setfill('*') << std::setw(26) << " " << endl; // First line of "*"
std::cout << "*" << std::setfill(' ') << std::setw(16) << "12 Hour Clock" << std::setfill(' ') << std::setw(4) << " *" << " "
<< "*" << std::setfill(' ') << std::setw(18) << "24 Hour Clock" << std::setfill(' ') << std::setw(6) << " *" << endl;
// 12 hour clock
std::cout << "*" << std::setfill(' ') << std::setw(6) << " " << time << std::setfill(' ') << std::setw(6) << " *" << " "
// 24 hour clock
<< "*" << std::setfill(' ') << std::setw(8) << " " << std::setfill(' ') << std::setw(8) << " *" << endl;
std::cout << std::setfill('*') << std::setw(26) << " " << std::setfill('*') << std::setw(26) << " " << endl; // Last line of "*"
return 0;
}
void DisplaySelection() { // Function to display selection menu for user
std::cout << std::setfill('*') << std::setw(26) << " " << endl;
std::cout << "*" << std::setfill(' ') << std::setw(19) << "1 - Add One Hour" << std::setfill(' ') << std::setw(5) << " *" << endl;
std::cout << "*" << std::setfill(' ') << std::setw(20) << "2 - Add One Minute" << std::setfill(' ') << std::setw(4) << " *" << endl;
std::cout << "*" << std::setfill(' ') << std::setw(20) << "3 - Add One Second" << std::setfill(' ') << std::setw(4) << " *" << endl;
std::cout << "*" << std::setfill(' ') << std::setw(19) << "4 - Exit Program" << std::setfill(' ') << std::setw(5) << " *" << endl;
std::cout << std::setfill('*') << std::setw(26) << " " << endl;
}
void main()
{
time_t now = time(0);
system("CLS");
string userVal;
DisplayClocks(now); // Call displayClocks on program start
DisplaySelection(); // Call DisplaySelection after display clocks
cin >> userVal; // Take user input to modify clock display
while (!( userVal == "Exit")) {
// FIX ME: Add functionality to clear screen every second
// FIX ME: Add displayClock to relevant if statements
if (userVal == "1") {
// Add One Hour to Clocks
// FIX ME: Functionality for Displaying 12 and 24 hour clocks
system("CLS"); // Clear screen test... working...
DisplayClocks(now); // Call displayClocks on program start
DisplaySelection(); // Call DisplaySelection after display clocks
cout << "1" << endl;
cin >> userVal;
}
else if (userVal == "2") {
// Add One Minute to Clocks
// FIX ME: Functionality for Displaying 12 and 24 hour clocks
system("CLS"); // Clear screen test... working...
DisplayClocks(now); // Call displayClocks on program start
DisplaySelection(); // Call DisplaySelection after display clocks
cout << "2" << endl;
cin >> userVal;
}
else if (userVal == "3") {
// Add One Second to Clocks
// FIX ME: Functionality for Displaying 12 and 24 hour clocks
system("CLS"); // Clear screen test... working...
DisplayClocks(now); // Call displayClocks on program start
DisplaySelection(); // Call DisplaySelection after display clocks
cout << "3" << endl;
cin >> userVal;
}
else if (userVal == "4") {
// Exit Program
// FIX ME: Functionality for Displaying 12 and 24 hour clocks
cout << "Program Ended" << endl;
break;
}
else{
// Prompt user to input correct selection when not userVal ! (1-4)
system("CLS"); // Clear screen test... working...
DisplayClocks(now);
DisplaySelection();
cout << "Error: Enter a selection 1 - 4." << endl;
cin >> userVal;
}
}
}

Answer 1

When you ask "How can I change SYSTEM <anything> in C++?", the keyword is "system".
It means that it's platform-dependent, so it needs a SYSTEM call - and I'm not speaking about the system function, but a call to your operating system's API, Win32 in your case. And a lot of these functions will requires elevation to work, on both Windows and Linux...
Unfortunately for you, changing system date and time is such a function, on both OS, and it isn't allowed to call it with a standard account.
Also, it has nothing related with C++, in fact. On Windows, you'll need to call SetSystemTime, and it's not a C++ feature but a function of kernel32.dll imported through sysinfoapi.h header (found in Windows SDK).
You'll get exactly the same answer in near any programming language: "Do a system call to SetSystemTime".