FreeConsole() does not detach application from cmd - c++

Question

I launch my application in cmd. I compiled it by Cmake without WIN32_EXECUTABLE, so it hangs in cmd (i.e. is launched as not detached). Now I want to close the console and try to achieve this by calling FreeConsole().
This works in case I double-click the application -- the black console is flashes quickly and gets closed. But it does not work when I launch it in cmd. The cmd is still attached to the launched application and FreeConsole() does not help.
Is there any way to detach it from cmd programmatically? I have found the opportunity to run start /b myapp, but I would like to do it in a programmatical way.
UPDATE
A rough implementation of the answer of Anders for those who are interested -- see below. In this implementation I pass all the arguments, supplied to main.com, to the child process main.exe.
// main.cpp
// cl main.cpp
// link main.obj /SUBSYSTEM:WINDOWS /ENTRY:"mainCRTStartup"
//
#include <stdio.h>
#include <Windows.h>
int main(int argc, char** argv)
{
if (AttachConsole(ATTACH_PARENT_PROCESS)) {
freopen("CONOUT$", "w", stdout);
freopen("CONOUT$", "w", stderr);
freopen("CONIN$", "r", stdin);
}
for (int i = 0; i < argc; i++)
printf("--%s", argv[i]);
printf("Hello\n");
int k = 0;
scanf("%d", &k);
printf("%d\n", k);
return 0;
}
// helper.cpp
// cl helper.cpp
// link helper.obj /OUT:main.com
//
#include <windows.h>
#include <stdio.h>
#include <string.h>
void main( int argc, char **argv )
{
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory( &si, sizeof(si) );
si.cb = sizeof(si);
ZeroMemory( &pi, sizeof(pi) );
// Reconstructing the command line args for main.exe:
char cmdLine[32767] = { 0 };
strcpy(cmdLine, "main.exe ");
int shift = strlen("main.exe ");
for (int i = 1 ; i < argc; i++)
{
strcpy(cmdLine + shift, argv[i]);
const int argLength = strlen(argv[i]);
cmdLine[shift + argLength] = ' ';
shift += (argLength + 1);
}
printf("\n!!!!%s!!!!!%s\n", cmdLine, GetCommandLine());
// Start the child process.
// https://learn.microsoft.com/en-us/windows/win32/procthread/creating-processes
//
if( !CreateProcess(NULL, // No module name (use command line)
cmdLine, // Command line
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si, // Pointer to STARTUPINFO structure
&pi ) // Pointer to PROCESS_INFORMATION structure
)
{
printf( "CreateProcess failed (%d).\n", GetLastError() );
return;
}
// Wait until child process exits.
WaitForSingleObject( pi.hProcess, INFINITE );
// Close process and thread handles.
CloseHandle( pi.hProcess );
CloseHandle( pi.hThread );
}

Answer 1

Creating a "perfect" application that can be both GUI or console is not possible on Windows.
When a .exe has its subsystem set to console, two things happen:
CreateProcess will attach it to the parents console. If the parent does not have one, a new console is created. This can only be suppressed by passing flags to CreateProcess.
cmd.exe will wait for the process to finish.
The trick of setting the subsystem to Windows and using AttachConsole is sub-optimal because cmd.exe will not wait.
The best solution is to create your main .exe as a Windows application. Create another console helper application that you rename from .exe to .com. The helper application will just launch the main app in GUI mode and then quit. In console mode it has to tell the main app that it needs to attach and you need to WaitForSingleObject on it. Example application available here .
Visual Studio uses this .com trick. The trick works because .com is listed before .exe in %pathext%.