write to com port and read answer immediately in c++ windows7 - c++

Question

I have a measurment device and want to make a series of measurments and store them to a file.
For this I need to read out the com port properly. All I get back with this code is some weird signs.
#include <windows.h>
#include <process.h>
#include <stdio.h>
#include <iostream>
#include <string>
using namespace std;
int main() {
// opening the serial port
HANDLE hSerial;
fprintf(stderr, "Opening serial port...");
hSerial = CreateFile("\\\\.\\COM2",
GENERIC_READ | GENERIC_WRITE, 0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
if (hSerial == INVALID_HANDLE_VALUE) {
fprintf(stderr, "Error\n");
CloseHandle(hSerial);
return 1;
} else
fprintf(stderr, "OK\n");
// settings to communicate with device
DCB dcbSerialParams;
ZeroMemory(&dcbSerialParams, sizeof(dcbSerialParams));
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
if (!GetCommState(hSerial, &dcbSerialParams)) {
//error getting state
fprintf(stderr,"error getting state ... ");
}
dcbSerialParams.BaudRate = 9600;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if (!SetCommState(hSerial, &dcbSerialParams)) {
//error setting state
fprintf(stderr,"error setting state ...");
}
char out_message[] = "fetch?"; // request for the device to send voltage and
current
char in_message[32];
DWORD BytesToWrite = sizeof(out_message);
DWORD BytesWritten;
DWORD BytesToRead = sizeof(in_message);
DWORD BytesRead;
WriteFile(hSerial, out_message, BytesToWrite, &BytesWritten, NULL);
ReadFile(hSerial, &in_message, BytesToRead, &BytesRead, NULL);
string buffer;
for (unsigned int i = 0; i < sizeof(in_message); i++) {
buffer += in_message[i];
}
buffer[sizeof(in_message) - 1] = '\0';
// try outs of different outputs
cout << buffer << "\n";
const char*c = buffer.c_str();
printf("%s\n",c);
CloseHandle(hSerial);
return 0;
}
I guess I cannot write to com an read out immediately?
Or is there a mistake in the conversion in_message to buffer?