shutdown command problem

[patr1ck]

How correctly put variable in shutdown command?

...
 system("shutdown -s -t //variable//");
...

[Ganado]

Can the origin of the variable be a string? Or must it be a numeric value?

If it can be a string, you can do:

#include <string> 
#include <cstdlib>

int main()
{
    std::string variable = "10";
    std::string command = "shutdown -s -t " + variable;
    system(command.c_str()); // c_str() returns a const char* to the string
}

However, if variable needs to be an integer, you have to convert it to a string.

With modern C++11, the answer is easy:

#include <string> 
#include <cstdlib>

int main()
{
    int variable = 10;
    std::string command = "shutdown -s -t " + std::to_string(variable);
    system(command.c_str());
}

pre-C++11:

#include <string>
#include <sstream> 
#include <cstdlib>

int main()
{
    std::stringstream ss;
    int variable = 10;
    ss << variable;
    std::string command = "shutdown -s -t " + ss.str();
    system(command.c_str());
}

[patr1ck]

Variable needs to be integer, I included your second idea but there's still something I messed up.

I'll paste whole code to show you what I'm trying to do (I'm beginner at programing ;) )

#include <iostream>
#include <windows.h>
#include <cstdlib>
#include <conio.h>

using namespace std;

int hours, minutes, time;
string choice;

int main()
{
    cout << " Hours: ";
    cin >> hours;
    cout <<endl;
    cout << " Minutes: ";
    cin >> minutes;
    cout <<endl;
    cout << " Are you sure? (Y/N): ";
    cin >> choice;

    if(choice == "Y" || "y")
    {
        hours=hours * 3600;
        minutes=minutes * 60;
        time= hours + minutes;
        string command_auto_off = "shutdown -s -t" + to_string(time);
        system(command_auto_off.c_str());
        system("cls");
        cout << " Done!";
    }

    if(choice == "N" || "n")
    {
        exit(0);
    }
    return 0;
}

The problem is with 27th line error: 'to_string' was not declared in this scope


I don't really know how to fix it. Thanks for the reply!

[JLBorges]

> error: 'to_string' was not declared in this scope

#include <string>

[patr1ck]

Still the same

[JLBorges]

std::to_string requires C++11 or later.

This (using a string stream to perform the conversion) will work with legacy C++
and also with broken GNU libraries (on Windows)

#include <iostream>
#include <cstdlib>
#include <string>
#include <sstream>

int main()
{
    int hours ;
    std::cout << " Hours: ";
    std::cin >> hours;

    int minutes ;
    std::cout << " Minutes: ";
    std::cin >> minutes;

    char choice ;
    std::cout << " Are you sure? (Y/N): ";
    std::cin >> choice;

    const int secs = hours*3600 + minutes*60 ;

    if( ( choice == 'Y' || choice == 'y' ) && secs >= 0 )
    {
        std::stringstream sstm ;
        sstm << secs ;
        std::string secs_str ;
        sstm >> secs_str ;

        const std::string command_auto_off = "shutdown -s -t " + secs_str ;
        std::system( command_auto_off.c_str() );
        std::cout << " Done!";
    }
}

[patr1ck]

Everything works, thank you! :)

I'm using Code Blocks, GNU GCC Compiler, that's the problem why previous solution didn't work?

[Ganado]

My third option should have worked, but it's pretty much equivalent to JLBorges'.

Regardless, there's some history to this because:
(1) Code Blocks may come with a slightly outdated compiler. I'm not sure if this is still the case, but the default compiler can easily be replaced with your own, up-to-date one -- Code Blocks as an IDE itself is still great.
(2) Outdated versions of the compiler have to set -std=c++11 as an addition command-line argument to g++ to get C++11 to work. There should be a checkbox in Compiler Settings that does this for you.
(3) Outdated versions of MinGW (Which is the GNU GCC Compiler for Windows) have a bug where std::to_string is not recognized. https://stackoverflow.com/questions/12975341/to-string-is-not-a-member-of-std-says-g-mingw

tl;dr I would suggest downloading a more-recent compiler version, and setting the paths in Code Blocks to point to the new compiler's bin folder's .exe's
https://stackoverflow.com/questions/5604183/adding-compiler-to-codeblocks