c++ - Modem does not return my program's echo request -

1. typing at + [enter] on putty modem's com3 port gives me ok response.

2. i used char-sending-and-recieving program analyze putty's output when sends data.

3. at+[enter] makes putty send at\r through port.

(\r meaning carriage return ascii value of 13.)

4. i used program send same stream of chars com3 port.

5. modem didn't respond ok. doesn't send response program @ all. ever. not error messages.

6. (i tested program, , can recieve data right after sending data of own, unlikely didn't catch ok in time, since requested longer strings response - strings hard miss.)

7. (it has no problems communicating through ports program , putty.)

what cause this? how can recieve modem's ok response?

(i tested strings ending \n, \r\n , \n\r advised, in case. didn't work.)

code (ports com8 , com9 connected btw):

#include <iostream> #include <windows.h> #include <conio.h> using namespace std;    bool writecomport(lpctstr portspecifier, lpctstr data) ; int readbyte(lpctstr portspecifier) ; void transciever( lpctstr portspecifier ) ;   int main () {     lpctstr portspecifier = "" ;     string temp = "" ;          {         cout << "\ncom8 or com9 or com3? " ;         getline(cin,temp) ;         if( temp == "com8" || temp == "com9" || temp == "com3" ) portspecifier = temp.c_str() ;      } while( temp != "com8" && temp != "com9" && temp != "com3" ) ;      transciever(portspecifier) ;        cout << "[program terminated.]\n" ;      cin.get() ;     return 0 ; }    void transciever(lpctstr portspecifier ) {     string text ;     lpcstr data ;     bool writesuccess = true ;     char output ;          {         if( _kbhit() )         {             text = _getch() ;             data =  text.c_str() ;              writesuccess = writecomport(portspecifier,data) ;              if(!writesuccess) cout << "[sending error.]\n" ;             else             {                 cout << text ;             }         }          output = (char) readbyte(portspecifier) ;         if( output != '_' )         {             cout << output ;              if( output == '=' )             {                 data =  "*" ;                 writesuccess = writecomport(portspecifier,data) ;                  if(!writesuccess) cout << "\n[    fail: sending * autoresponse = ]\n" ;                              else cout << "\n[ success: sending * autoresponse = ]\n" ;             }         }      } while( text != "#" && output != '#' ) ; }    bool writecomport(lpctstr portspecifier, lpctstr data) {     dcb dcb;     dword       byteswritten;      handle hport = createfile( portspecifier,                                generic_write,                                0,                                null,                                open_existing,                                0,                                null );         if (!getcommstate(hport,&dcb))        {            cout << "failed getting " << portspecifier << " port's state.\n" ;            return       false;        }         dcb.baudrate = cbr_9600;          //9600 baud        dcb.bytesize = 7;                 //7 data bits        dcb.parity = true;        dcb.stopbits = onestopbit;        //1 stop         if (!setcommstate(hport,&dcb))        {            cout << "[failed setting " << portspecifier << "'s state.]\n" ;            return false ;        }         int bytestowrite = 1 ;         bool retval = writefile(hport,data,bytestowrite,&byteswritten,null);         closehandle(hport); //close handle         return  retval; }    int readbyte(lpctstr portspecifier) {     dcb dcb;     int retval;     byte byte = '_' ;     dword dwbytestransferred;     handle hport = createfile     (         portspecifier,         generic_read,         0,         null,         open_existing,         0,         null     );     if (!getcommstate(hport,&dcb))     {         cout << "\n[getcommstate fail]\n" ;         return '_' ;     }      commtimeouts timeouts={0};     timeouts.readintervaltimeout=50;     timeouts.readtotaltimeoutconstant=50;     timeouts.readtotaltimeoutmultiplier=10;     timeouts.writetotaltimeoutconstant=50;     timeouts.writetotaltimeoutmultiplier=10;      if(!setcommtimeouts(hport, &timeouts))     {         cout << "\n[setcommtimeouts fail]\n" ;         return '_' ;     }      dcb.baudrate = cbr_9600; //9600 baud     dcb.bytesize = 7; //7 data bits     dcb.parity = true; //parity     dcb.stopbits = onestopbit; //1 stop      if (!setcommstate(hport,&dcb))     {         cout << "\n[setcommstate fail]\n" ;         return '_' ;     }      if (!setcommmask (hport, ev_rxchar | ev_err) )     {         cout << "\n[setcommmask fail]\n" ;         return '_' ;     }      if( !readfile (hport, &byte, 1, &dwbytestransferred, 0) )     {         cout << "\n[readfile fail]\n" ;         return '_' ;     }      retval = byte;     if (!closehandle(hport))     {         cout << "\n[closehandle fail]\n" ;         return '_' ;     }     return retval; } 

.

also alternative version of readbyte, reads many bytes @ once:

string readbyte(lpctstr portspecifier) {     dcb dcb;     dword dwbytestransferred;     handle hport = createfile     (         portspecifier,         generic_read,         0,         null,         open_existing,         0,         null     );     if (!getcommstate(hport,&dcb))     {         cout << "\n[readbyte: getcommstate fail]\n" ;         return "-1" ;     }      commtimeouts timeouts={0};     timeouts.readintervaltimeout=50;     timeouts.readtotaltimeoutconstant=50;     timeouts.readtotaltimeoutmultiplier=10;     timeouts.writetotaltimeoutconstant=50;     timeouts.writetotaltimeoutmultiplier=10;      if(!setcommtimeouts(hport, &timeouts))     {         cout << "\n[readbyte: setcommtimeouts fail]\n" ;         return "-1" ;     }      dcb.baudrate = cbr_9600; //9600 baud     dcb.bytesize = 7; //7 data bits     dcb.parity = evenparity; //parity     dcb.stopbits = onestopbit; //1 stop      if (!setcommstate(hport,&dcb))     {         cout << "\n[readbyte: setcommstate fail]\n" ;         return "-1" ;     }      if (!setcommmask (hport, ev_rxchar | ev_err) )     {         cout << "\n[readbyte: setcommmask fail]\n" ;         return "-1" ;     }      const int bytestoread = 30 ;     char messagerecieved[bytestoread+1] = {0};     //&byte      if( !readfile (hport, &messagerecieved, bytestoread, &dwbytestransferred, 0) )     {         cout << "\n[readbyte: readfile fail]\n" ;         return "-1" ;     }        if (!closehandle(hport))     {         cout << "\n[readbyte: closehandle fail]\n" ;         return "-1" ;     }      if( dwbytestransferred == bytestoread )     {         cout << "\n[readbyte: possible message cut off @ end." ;     }      return string(messagerecieved) ; }