Kill Process

The debug API is an old trick for killing processes you do not own in the normal sense: DebugActiveProcess attaches your program as the debugger of the target, which suspends it, and once attached the target can be ended through the debug event loop. This snippet asks for a PID on the command line, attaches, and waits on the first debug event (the initial suspend) before returning - at which point the attach/teardown has done its work. It requires the target to be debuggable (not protected, same or lower integrity) and is best understood as a curiosity/utility from the Windows 9x era rather than a production kill mechanism; modern code should prefer OpenProcess(PROCESS_TERMINATE) + TerminateProcess.

#include <windows.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    DEBUG_EVENT DE;
    long ProcID;
    char CmdLine[257];

    printf("%s\n","Process Termination using DebugActiveProcess");
    printf("Process ID: ");

    gets(CmdLine);
    ProcID = atof(CmdLine);

    if ( DebugActiveProcess(ProcID) == 0 )
    {
        printf("%s\n","Error - couldn't attach to process.");
    }
    else {
        printf("%s\n","Attached to process - terminating ...");
    }

    WaitForDebugEvent(&DE, 0);
    return TRUE;
}

Note the use of gets, which is unsafe and removed from modern standard libraries - replace with fgets(CmdLine, sizeof(CmdLine), stdin) if you build this today.