After I get a handle returned by CreateProcess, I call TerminateProcess, passing 42 for the process exit code. Then, I use WaitForSingleObject for the process to terminate, and finally I call GetExitCodeProcess.

None of the function calls report errors. The child process is an infinite loop and does not terminate on its own.

The problem is that sometimes GetExitCodeProcess returns 42 for the exit code (as it should) and sometimes it returns 0. Any idea why?

#include <string>
#include <sstream>
#include <iostream>
#include <assert.h>
#include <windows.h>

void check_call( bool result, char const * call );
#define CHECK_CALL(call) check_call(call,#call);

int
main( int argc, char const * argv[] )
    {
    if( argc>1 )
        {
        assert( !strcmp(argv[1],"inf") );
        for(;;)
            {
            }
        }
    int err=0;
    for( int i=0; i!=200; ++i )
        {
        STARTUPINFO sinfo;
        ZeroMemory(&sinfo,sizeof(STARTUPINFO));
        sinfo.cb=sizeof(STARTUPINFO);
        PROCESS_INFORMATION pe;
        char cmd_line[32768];
        strcat(strcpy(cmd_line,argv[0])," inf");
        CHECK_CALL((CreateProcess(0,cmd_line,0,0,TRUE,0,0,0,&sinfo,&pe)!=0));
        CHECK_CALL((CloseHandle(pe.hThread)!=0));
        CHECK_CALL((TerminateProcess(pe.hProcess,42)!=0));
        CHECK_CALL((WaitForSingleObject(pe.hProcess,INFINITE)==WAIT_OBJECT_0));
        DWORD ec=0;
        CHECK_CALL((GetExitCodeProcess(pe.hProcess,&ec)!=0));
        CHECK_CALL((CloseHandle(pe.hProcess)!=0));
        err += (ec!=42);
        }
    std::cout << err;
    return 0;
    }

std::string
get_last_error_str( DWORD err )
    {
    std::ostringstream s;
    s << err;
    LPVOID lpMsgBuf=0;
    if( FormatMessageA(
            FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
            0,
            err,
            MAKELANGID(LANG_NEUTRAL,SUBLANG_DEFAULT),
            (LPSTR)&lpMsgBuf,
            0,
            0) )
        {
        assert(lpMsgBuf!=0);
        std::string msg;
        try
            {
            std::string((LPCSTR)lpMsgBuf).swap(msg);
            }
        catch(
        ... )
            {
            }
        LocalFree(lpMsgBuf);
        if( !msg.empty() && msg[msg.size()-1]=='\n' )
            msg.resize(msg.size()-1);
        if( !msg.empty() && msg[msg.size()-1]=='\r' )
            msg.resize(msg.size()-1);
        s << ", \"" << msg << '"';
        }
    return s.str();
    }

void
check_call( bool result, char const * call )
    {
    assert(call && *call);
    if( !result )
        {
        std::cerr << call << " failed.\nGetLastError:" << get_last_error_str(GetLastError()) << std::endl;
        exit(2);
        }
    }