Creating object in C++ , what if already constructed? - c++

Question

I am still new to c++. I want to read in messages from several sources. Each source will begin data messages with a 4 char ID. Each will also have several data messages. No one message has all of the info I want from the device. So if I create an object with the ID as the object name, the next time a message is received, will the object be updated or completely reconstructed? Is there a way to check if the object is already constructed before calling it in the code?
class Channels{
public:
INT8U systemID; //0x01 Glonass, 0x02 GPS
INT8U satID;
INT8U GlonassNumber;
INT8U SNR; //signal to noise ratio
FP64 carrierPhase; //cylces
FP64 psuedoRange; //milliseconds
FP64 doppler; //HZ cycles
float tropDelay; //meters
float ionoDelay; //meters
};
class BaseStation{
public:
Channels channel[32]; //each channel object has all channel class variables in it
int numberSatelitesTracked;
FP64 timeUTC;
INT16U week;
FP64 GPStoUTCoffset;
FP64 GLOtoUTCoffset;
INT8S recieverTimeOffset;
FP64 posX; //geocentric coordinates in meters
FP64 posY;
FP64 posZ;
FP64 rmsX; //expected root mean square error of coordinates
FP64 rmsY;
FP64 rmsZ;
};
if( check == SOCKET_ERROR){
if( WSAGetLastError() != WSAEWOULDBLOCK){
printf("base station client recieve failed with error %d \n", WSAGetLastError());
FreeSocketInformation(i); //shuts down client socket if no data
}
continue;
}
else{
//recieve bytes into array
memcpy(recvArray, SocketInfo->DataBuf.buf, SocketInfo->RecvBytes +1);
//print recieved bytes on screen
printf("%s \n", SocketInfo->DataBuf.buf);
//first 4 bytes in message are base ID
cBuffer[0] = recvArray[0];
cBuffer[1] = recvArray[1];
cBuffer[2] = recvArray[2];
cBuffer[3] = recvArray[3];
baseID = cBuffer;
//create object with 4 char name
BaseStation baseID;
//test message identity and sort data
if(recvArray[4] == 0x10 && recvArray[5] == 0xF5){
baseID.timeUTC = combine64(recvArray[6]);
baseID.week = combine16u(recvArray[14]);
baseID.GPStoUTCoffset = combine64(recvArray[16]);
baseID.GLOtoUTCoffset = combine64(recvArray[24]);
baseID.recieverTimeOffset = recvArray[32];
int noChannels = (check-30) /30 ;
if (noChannels >= 32){
noChannels = 32;
}
int x = 33;
for(int m = 0; m < noChannels; m++){ //advance reading for channel m
baseID.channel[m].systemID = recvArray[x];
x++;
baseID.channel[m].satID = recvArray[x];
x++;
baseID.channel[m].GlonassNumber = recvArray[x];
x++;
baseID.channel[m].SNR = recvArray[x];
x++;
baseID.channel[m].carrierPhase = combine64(recvArray[x]);
x = x+8;
baseID.channel[m].psuedoRange = combine64(recvArray[x]);
x = x+8;
baseID.channel[m].doppler = combine64(recvArray[x]);
x = x+10;
} //end of for loop to gather F5 sat data
} //end F5 message data
if(recvArray[4] == 0x10 && recvArray[5] == 0xF6){
baseID.posX = combine64(recvArray[6]);
baseID.posY = combine64(recvArray[14]);
baseID.posZ = combine64(recvArray[22]);
baseID.rmsX = combine64(recvArray[30]);
baseID.rmsY = combine64(recvArray[38]);
baseID.rmsZ = combine64(recvArray[46]);
} //end F6 message data
OK so it seems an Array may be the best for me to use. So if I setup 100 base objects and then track the active array elements with a second boolean array, does this look like it should work? (baseID added to the base object)
BaseStation base[100];
boolean baseActive[100];
int baseNumber;
//begin message processing------------------------------------------------------------
//first 4 bytes in message are base ID
cBuffer[0] = recvArray[0];
cBuffer[1] = recvArray[1];
cBuffer[2] = recvArray[2];
cBuffer[3] = recvArray[3];
string name = cBuffer;
//check for existing baseID------------------------------------------------------------
// 100 array positions
//find if base is already in use, create new if not in use
for(baseNumber = 0; base[baseNumber].baseID != name; baseNumber++){
//for statement increases untill it finds baseID == name
if( baseNumber >= 100){ //baseID not currently in use
for(int n=0; baseActive[n] == true; n++){
//for statement increases untill finds a false baseActive
baseNumber = n; //assign baseNumber to the array position
base[baseNumber].baseID = name; //create new baseID
continue;
}
}
}
//check and process message data--------------------------------------------------------
if( base[baseNumber].baseID == name){
baseActive[baseNumber] = true;
//test message identity and sort data
}//end of for loop
//test connection, if no bytes recieved then connection is closed.----------------------
if( SocketInfo->RecvBytes == 0){
FreeSocketInformation(i); //shuts down client socket if no data
continue;
}
}
} //end of read data from socket
}
//need to add a timer to remove non sending bases from the baseActive[] array

Answer 1

C++ is a statically typed language, You need to provide the object name at compile time.
You cannot create an object name at run-time and create object with that name.

Answer 2

As already answered, you can't do so in C++.
However you can solve your problem in other way.
First, you need to bind some ID to some concrete object of structure BaseStation. You can provide this link in two ways - by holding BaseStation objects in associative containter, where keys are ID, or by holding array of BaseStation objects(as far as I can guess you are writing some sort of microcontroller code so std containers can be not available for you).
First approach code example:
//id is 4 char so it can be thought as int on most systems
std::map<int, BaseStation *> baseStations;
int * id = (int*)recvArray; //this hack is for showing how you can convert 4 char to int
//may be in your code (int id = combine32(recvArray[0])) is equvivalent
if(baseStations.find(*id) != baseStations.end()) //checking existance of object with such id
{
//ok, exists, do nothing
}
else
baseStations[*id] = new BaseStation(); //create new
baseStations[*id].timeUTC = combine64(recvArray[6]); //starting copying values
//other values copying
In second situation if you can't use associative containers or can't afford their libs\code because of microcontroller memory lack, you can use just arrays but it's not flexible at all and consumes more operations. Example:
//BaseConnection also holds field names id;
BaseConnection baseConnections[N];
int FindId(int id); //return index of element in baseConnections array with this id
BaseConnection * workingConnection = &baseConnections[FindId(combine32(recvArray[0]))];
workingConnection->timeUTC = combine64(recvArray[6]); //starting copying values
//other values copying