#include <iostream>
#include <windows.h>
using namespace std;
int main(){
LPWSTR test = L"C:/aizen.png";
int result = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, test, SPIF_UPDATEINIFILE);
if(result)
cout << "Wallpaper set!";
else
cout << "NOOOOO!" << result;
cin >> result;
return 0;
}
Very simple code, but result returns 0. What am I doing wrong?
Do what the documentation says, and call GetLastError to find out the reason behind the error.
Some possible causes spring to mind:
SystemParametersInfo does not like forward slashes as separators.
The system doesn't like .png files for wallpaper.
The file doesn't exist.
You have an ANSI/Unicode encoding mismatch.
You don't have rights to modify the wallpaper.
Really, the list is endless. So let the system tell you.
Note that the documentation says:
When the SPI_SETDESKWALLPAPER flag is used, SystemParametersInfo always returns TRUE.
But this is a great big fat lie. It's trivially easy to call the function, pass SPI_SETDESKWALLPAPER, and receive FALSE in return.
Don't know with the information we have.
This return value indicates that the call failed. You'll need to call GetLastError() for information about why.
Related
I want to write some code in C++ in combination with windows API in order to change the input method on windows (Keyboard input language).
Here is my first try:
#include <iostream>
#include <windows.h>
int main() {
int arr_size = GetKeyboardLayoutList(0, NULL);
HKL hkl_array[arr_size]; // The array to hold input locale identifies found in the system(HKL)
// Initialize the array to all zeros
for (int i = 0; i <= arr_size - 1; i++) {
hkl_array[i] = nullptr;
}
int lang_found = GetKeyboardLayoutList(arr_size, hkl_array); // Get all the HKLs in the array
for (int i = 0; i <= lang_found - 1; ++i) {
// Print all the HKLs found
std::cout << i + 1 << ". " << hkl_array[i] << std::endl;
}
std::cout << "Function return: " << ActivateKeyboardLayout(hkl_array[0], KLF_SETFORPROCESS);
return 0;
}
When running the above code with English as the current language I get:
1. 0x4080408
2. 0x4090409
Function return: 0x4090409
(0x4080408 is Greek and 0x4090409 is English)
According to the documentation for ActivateKeyboardLayout, the return value is of type HKL and If the function succeeds, the return value is the previous input locale identifier. Otherwise, it is zero. In my case, the function clearly runs with no errors since it returns the input locale identifier for English witch was the language before the hypothetical change. The language although does not change. I get similar results if I start from greek and try to change to English.
I have tried different values in the flag parameter with no luck. It is always the same thing. I have also tried using the LoadKeyboardLayoutA as follows:
#include <iostream>
#include <windows.h>
int main(){
LPCSTR language_select = "00000408"; // Code for greek
std::cout << LoadKeyboardLayoutA(language_select, KLF_ACTIVATE);
return 0;
}
When running the above code with English as the current language I get:
0x4080408
According to the documentation for LoadKeyboardLayoutA, If the function succeeds, the return type is HKL and the return value is the input locale identifier corresponding to the name specified in the function's parameter (language_select). So this seems to run ok as well but no luck with language change. I also tried with language_select = "00000809" (UK English) and the result I got was Uk English was just added to the list of languages as I did not have it installed.
Finally, I tried calling the ActivateKeyboardLayout with LoadKeyboardLayoutA ad the HKL parameter as follows
#include <iostream>
#include <windows.h>
int main() {
LPCSTR language_select = "00000408"; // Code for greek
std::cout << ActivateKeyboardLayout(LoadKeyboardLayoutA(language_select, KLF_ACTIVATE), KLF_SETFORPROCESS);
return 0;
}
When running the above code with English as the current language I get:
0x4080408
Which again seems normal but there is no chance in the language. I am running this on Windows 10 20H2 OS Build 19042.685 and I am using CLion as an IDE (I don't think it matters but just in case anyone needs the info). What am I doing wrong?
The very first sentence of the ActivateKeyboardLayout function documentation states: "Sets the input locale identifier (formerly called the keyboard layout handle) for the calling thread or the current process.". Since you never read input in your program, you don't observe its effect. It does not change the keyboard layout of the system.
On Windows, each thread has its own keyboard layout. To change the keyboard layout for a specific window, you need to send the WM_INPUTLANGCHANGEREQUEST message to it:
SendMessageW(<windowHandle>, WM_INPUTLANGCHANGEREQUEST, 0, LoadKeyboardLayoutW(language_select, KLF_ACTIVATE));
First of all, I understand there are many topics on this function, but I did not find any about this particular problem, sorry if I am repeating...
I have been working on a program in C++ that works with printers and I need to get the list of printers in the system.
I am using the EnumPrinters API and I am getting a compile error I don't understand.
This is my code:
#include <iostream>
#include <windows.h>
#include <winspool.h>
using namespace std;
int main()
{
PRINTER_INFO_5 pi;
PBYTE buffer[99];
DWORD bufferSize = 0;
DWORD bufferNeeded = 0;
DWORD Entries = 0;
bool r;
r = EnumPrinters(PRINTER_ENUM_LOCAL | PRINTER_ENUM_CONNECTIONS, NULL, 5, NULL, bufferSize, &bufferNeeded, &Entries);
if (!r)
{ cout << "No printer found" << endl; }
else { cout << "Found printers" << endl; }
}
When I try to compile (codeBlocks typical installation w/ gcc), I get this error:
C:\Programação\C++\lab\main.cpp 18 undefined reference to 'EnumPrintersA#28'
I think this may be a linker problem, but I don't know how to solve it...
Thank you!
SOLVED!
After some help I found out that the problem was that I wasn't importing the correct library. I thought including the header would be enough.
I needed to follow these steps (using 'winspool' instead of 'gdi32').
By the way, adding 'winspool.lib' did not solve it. Use 'winspool' instead (no '.lib')
Your linker is missing a .lib-file. If you lookup EnumPrinters at the MSDN documentation, you will see which library you have to add (somewhere at the bottom of the page, right before the comments).
In this case it's Winspool.lib. For gcc, add the commandline option: -lwinspool.
I wrote the program of finding file using FindFirstFile(...) function. But when I try to print the output of this function, there is a several strings of unknown characters printed in console windows.
I read some posts, there was written to try using wcout instead of cout. I try it, but it doesn't help. I think, that the problem is in difference between ANSI and UNICODE encodings. Can somebody help me? I will be very thankful for any help!
Here is my code:
#include "FindFile.h"
#include <iostream>
using namespace std;
void FindFileCl::Execute(Input * input, Response * response )
{
WIN32_FIND_DATAA FindFileData;
HANDLE h = FindFirstFileA((input->FileName).c_str(), // name of the file
&FindFileData);
if (h)
{
cout << "Search Results:\n";
cout<<(FindFileData.cFileName);
CloseHandle(h);
}
else
{
cerr << "File is NOT found:" << GetLastError() << "\n";
}
}
If FindFirstFile() fails it returns INVALID_HANDLE_VALUE, not NULL:
If the function fails or fails to locate files from the search string in the lpFileName parameter, the return value is INVALID_HANDLE_VALUE and the contents of lpFindFileData are indeterminate. To get extended error information, call the GetLastError function.
and INVALID_HANDLE_VALUE is #defined as -1 (following macro located in WinBase.h):
#define INVALID_HANDLE_VALUE ((HANDLE)(LONG_PTR)-1)
Meaning the if (h) will be entered in either success or failure. In the event of failure, cFileName will not be modified resulting in junk being printed as it is not initialized. Change the if condition to explicitly check for INVALID_HANDLE_VALUE:
if (h != INVALID_HANDLE_VALUE)
{
}
One of the "least bad" ways would be to convert the Unicode name to the Console's encoding.
For this, I suggest compiling in Unicode (There's a project option for that in Visual Studio >=8; otherwise you have to define both UNICODE and _UNICODE manually), using the TCHAR version of FindFirstFile(), and then using CharToOem() or CharToOemBuff() (neither is perfect). -- Or alternately, use the W version followed by WideCharToMultiByte(CP_OEMCP).
The program I am writing is a simple console application that gets params, computes, and then returns data.
I am asking this because I am trying to implement a smart "press enter to exit" message that would run only if a console program is called by clicking on its icon in explorer. Without it, the result is that program only flashes for a split of second, but if a program is run from a context of already opened console then the same thing becomes an annoyance. Similar thing arises when program is run inside bat or cmd file, then pausing at the end is also unwelcome since bat files have 'pause' command that is supposed to do it.
So, we have 2 modes:
program says "press enter to exit" when is started by:
direct clicking in explorer
clicking on a shortcut
Simply exit when:
its name is typed in console
it is run from a bat/cmd file
it is run from another console application
Using Windows APIs:
You can use the GetConsoleProcessList API function (available on Windows XP/2003 and higher only). It returns a list of processes that are attached to the current console. When your program is launched in the "no console" mode, your program is the only process attached to the current console. When your program is launched from another process which already has a console, there will be more than one process attached to the current console.
In this case, we don't care about the list of process IDs returned by the function, we only care about the count that is returned.
Example program (I used Visual C++ with a Console Application template):
#include "stdafx.h"
#include <iostream>
#include <Windows.h>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
DWORD procIDs[2];
DWORD maxCount = 2;
DWORD result = GetConsoleProcessList((LPDWORD)procIDs, maxCount);
cout << "Number of processes listed: " << result << endl;
if (result == 1)
{
system("pause");
}
return 0;
}
We only need to list up to 2 processes, because we only care whether there is 1 or more than 1.
Using Windows APIs present in Windows 2000:
GetConsoleWindow returns the window handle of the console associated with the current process (if any). GetWindowThreadProcessId can tell you which process created a window. And finally, GetCurrentProcessId tells you the id of current process. You can make some useful deductions based on this information:
#include "stdafx.h"
#include <iostream>
#include <Windows.h>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
HWND consoleWindow = GetConsoleWindow();
if (consoleWindow != NULL)
{
DWORD windowCreatorProcessId;
GetWindowThreadProcessId(consoleWindow, &windowCreatorProcessId);
if (windowCreatorProcessId == GetCurrentProcessId())
{
cout << "Console window was created by this process." << endl;
system("pause");
}
else
cout << "Console window was not created by this process." << endl;
}
else
cout << "No console window is associated with this process." << endl;
return 0;
}
This technique seems slightly less precise than the first one, but I think in practice it should perform equally well.
The simplest solution I can think of is require the first parameter to be a flag whether or not the program should pause at the end. If the parameter is not there, i.e. it was started via explorer and the user did not have the ability to pass it in, then it should pause.
//Pseudo-code!!
int main(int argc, char** argv) {
//...
if(argv[1] == SHOULD_PAUSE) system("pause");
return 0;
}
There's a simple way to do this, and of course a more complicated way. The more complicated way may be more fun in the end, but probably more trouble than it's worth.
For the simple way, add a command line argument to the program, --pause-on-exit or something similar. Pass the extra arg whan calling it from a batch-file or the launcher icon. You could of course rather check for an environment variable for a similar effect.
For a more complicated (and automatic) way, you could probably try to find out who is the parent process of your application. You may have to go further up the chain than your immediate parent, and it may not work in all cases. I'd go for the command line argument.
Elaborating on my comment, rather than trying to tell how the program was executed (which I don't know is even possible, I'd assume there's no difference/distinction at all), I would implement a similar functionality in either one of two ways:
Add an extra argument to the program that will either make it "pause" at the end before terminating or not. ie. You could have something like -w to make it wait, or -W to make it not wait, and default with not waiting (or vice versa). You can add arguments through shortcuts.
Add a timer at the end of the program so that you wait for a few seconds, long enough for the user to read the input, so that the program doesn't wait infinitely when used in a batch.
Visual Studio introduces a wrinkle to #tcovo's otherwise valid answer when you are debugging. In this situation, it creates a second process and attaches it to the same console as the process you're running in:
So, it's necessary to detect the debugger using the Windows API function IsDebuggerPresent in order to get a definitive answer:
#include <iostream>
#include <Windows.h>
#include "debugapi.h"
int main()
{
DWORD pl[2];
auto np = GetConsoleProcessList(pl, 2);
std::cout << np << " processes\n";
bool shared;
if (IsDebuggerPresent())
shared = np > 2;
else
shared = np > 1;
std::cout << "Shared: ";
std::boolalpha(std::cout);
std::cout << shared << "\n";
std::cin.ignore(1);
return 0;
}
This only matters if you're using the local debugger; when run in a remote debugger there is still only one process attached.
One of the first things I learned in C++ was that
#include <iostream>
int main()
{
std::cout<<"Hello, World!\n";
return 0;
}
would simply appear and disappear extremely quickly without pause. To prevent this, I had to go to notepad, and save
helloworld.exe
pause
ase
helloworld.bat
This got tedious when I needed to create a bunch of small test programs, and eventually I simply put while(true); at the end on most of my test programs, just so I could see the results. Is there a better wait function I can use?
you can require the user to hit enter before closing the program... something like this works.
#include <iostream>
int main()
{
std::cout << "Hello, World\n";
std::cin.ignore();
return 0;
}
The cin reads in user input, and the .ignore() function of cin tells the program to just ignore the input. The program will continue once the user hits enter.
Link
Please note that the code above was tested on Code::Blocks 12.11 and Visual Studio 2012
on Windows 7.
For forcing your programme stop or wait, you have several options :
sleep(unsigned int)
The value has to be a positive integer in millisecond.
That means that if you want your programme wait for 2 seconds, enter 2000.
Here's an example :
#include <iostream> //for using cout
#include <stdlib.h> //for using the function sleep
using namespace std; //for using cout
int main(void)
{
cout << "test" << endl;
sleep(5000); //make the programme waiting for 5 seconds
cout << "test" << endl;
sleep(2000); // wait for 2 seconds before closing
return 0;
}
If you wait too long, that probably means the parameter is in seconds. So change it to this:
sleep(5);
For those who get error message or problem using sleep try to replace it by _sleep or Sleep especially on Code::Bloks.
And if you still getting problems, try to add of one this library on the beginning of the code.
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <dos.h>
#include <windows.h>
system("PAUSE")
A simple "Hello world" programme on windows console application would probably close before you can see anything. That the case where you can use system("Pause").
#include <iostream>
using namespace std;
int main(void)
{
cout << "Hello world!" << endl;
system("PAUSE");
return 0;
}
If you get the message "error: 'system' was not declared in this scope" just add
the following line at the biggining of the code :
#include <cstdlib>
cin.ignore()
The same result can be reached by using cin.ignore() :
#include <iostream>
using namespace std;
int main(void)
{
cout << "Hello world!" << endl;
cin.ignore();
return 0;
}
cin.get()
example :
#include <iostream>
using namespace std;
int main(void)
{
cout << "Hello world!" << endl;
cin.get();
return 0;
}
getch()
Just don't forget to add the library conio.h :
#include <iostream>
#include <conio.h> //for using the function getch()
using namespace std;
int main(void)
{
cout << "Hello world!" << endl;
getch();
return 0;
}
You can have message telling you to use _getch() insted of getch
Lots of people have suggested POSIX sleep, Windows Sleep, Windows system("pause"), C++ cin.get()… there's even a DOS getch() in there, from roughly the late 1920s.
Please don't do any of these.
None of these solutions would pass code review in my team. That means, if you submitted this code for inclusion in our products, your commit would be blocked and you would be told to go and find another solution. (One might argue that things aren't so serious when you're just a hobbyist playing around, but I propose that developing good habits in your pet projects is what will make you a valued professional in a business organisation, and keep you hired.)
Keeping the console window open so you can read the output of your program is not the responsibility of your program! When you add a wait/sleep/block to the end of your program, you are violating the single responsibility principle, creating a massive abstraction leak, and obliterating the re-usability/chainability of your program. It no longer takes input and gives output — it blocks for transient usage reasons. This is very non-good.
Instead, you should configure your environment to keep the prompt open after your program has finished its work. Your Batch script wrapper is a good approach! I can see how it would be annoying to have to keep manually updating, and you can't invoke it from your IDE. You could make the script take the path to the program to execute as a parameter, and configure your IDE to invoke it instead of your program directly.
An interim, quick-start approach would be to change your IDE's run command from cmd.exe <myprogram> or <myprogram>, to cmd.exe /K <myprogram>. The /K switch to cmd.exe makes the prompt stay open after the program at the given path has terminated. This is going to be slightly more annoying than your Batch script solution, because now you have to type exit or click on the red 'X' when you're done reading your program's output, rather than just smacking the space bar.
I assume usage of an IDE, because otherwise you're already invoking from a command prompt, and this would not be a problem in the first place. Furthermore, I assume the use of Windows (based on detail given in the question), but this answer applies to any platform… which is, incidentally, half the point.
The appearance and disappearance of a window for displaying text is a feature of how you are running the program, not of C++.
Run in a persistent command line environment, or include windowing support in your program, or use sleep or wait on input as shown in other answers.
the equivalent to the batch program would be
#include<iostream>
int main()
{
std::cout<<"Hello, World!\n";
std::cin.get();
return 0;
}
The additional line does exactly what PAUSE does, waits for a single character input
There is a C++11 way of doing it. It is quite simple, and I believe it is portable. Of course, as Lightness Races in Orbit pointed out, you should not do this in order to be able to see an Hello World in your terminal, but there exist some good reason to use a wait function. Without further ado,
#include <chrono> // std::chrono::microseconds
#include <thread> // std::this_thread::sleep_for
std::this_thread::sleep_for(std::chrono::microseconds{});
More details are available here. See also sleep_until.
Actually, contrary to the other answers, I believe that OP's solution is the one that is most elegant.
Here's what you gain by using an external .bat wrapper:
The application obviously waits for user input, so it already does what you want.
You don't clutter the code with awkward calls. Who should wait? main()?
You don't need to deal with cross platform issues - see how many people suggested system("pause") here.
Without this, to test your executable in automatic way in black box testing model, you need to simulate the enter keypress (unless you do things mentioned in the footnote).
Perhaps most importantly - should any user want to run your application through terminal (cmd.exe on Windows platform), they don't want to wait, since they'll see the output anyway. With the .bat wrapper technique, they can decide whether to run the .bat (or .sh) wrapper, or run the executable directly.
Focusing on the last two points - with any other technique, I'd expect the program to offer at least --no-wait switch so that I, as the user, can use the application with all sort of operations such as piping the output, chaining it with other programs etc. These are part of normal CLI workflow, and adding waiting at the end when you're already inside a terminal just gets in the way and destroys user experience.
For these reasons, IMO .bat solution is the nicest here.
What you have can be written easier.
Instead of:
#include<iostream>
int main()
{
std::cout<<"Hello, World!\n";
return 0;
}
write
#include<iostream>
int main()
{
std::cout<<"Hello, World!\n";
system("PAUSE");
return 0;
}
The system function executes anything you give it as if it was written in the command prompt. It suspends execution of your program while the command is executing so you can do anything with it, you can even compile programs from your cpp program.
Syntax:
void sleep(unsigned seconds);
sleep() suspends execution for an interval (seconds).
With a call to sleep, the current program is suspended from execution for the number of seconds specified by the argument seconds. The interval is accurate only to the nearest hundredth of a second or to the accuracy of the operating system clock, whichever is less accurate.
This example should make it clear:
#include <dos.h>
#include <stdio.h>
#include <conio.h>
int main()
{
printf("Message 1\n");
sleep(2); //Parameter in sleep is in seconds
printf("Message 2 a two seconds after Message 1");
return 0;
}
Remember you have to #include dos.h
EDIT:
You could also use winAPI.
VOID WINAPI Sleep(
DWORD dwMilliseconds
);
Sleep Function(Windows)
Just a note,the parameter in the function provided by winapi is in milliseconds ,so the sleep line at the code snippet above would look like this "Sleep(2000);"
getchar() provides a simplistic answer (waits for keyboard input).
Call Sleep(milliseconds) to sleep before exit.
Sleep function (MSDN)
You can use sleep() or usleep().
// Wait 5 seconds
sleep( 5 );
Well, this is an old post but I will just contribute to the question -- someone may find it useful later:
adding 'cin.get();' function just before the return of the main() seems to always stop the program from exiting before printing the results: see sample code below:
int main(){
string fname, lname;
//ask user to enter name first and last name
cout << "Please enter your first name: ";
cin >> fname;
cout << "Please enter your last name: ";
cin >> lname;
cout << "\n\n\n\nyour first name is: " << fname << "\nyour last name is: "
<< lname <<endl;
//stop program from exiting before printing results on the screen
cin.get();
return 0;
}
Before the return statement in you main, insert this code:
system("pause");
This will hold the console until you hit a key.
#include<iostream>
#include<string>
using namespace std;
int main()
{
string s;
cout << "Please enter your first name followed by a newline\n";
cin >> s;
cout << "Hello, " << s << '\n';
system("pause");
return 0; // this return statement isn't necessary
}
The second thing to learn (one would argue that this should be the first) is the command line interface of your OS and compiler/linker flags and switches.