How to write back to a csv file that was just read (c++)?

How to write back to a csv file that was just read (c++)?

Im trying to write back to a csv file that was previously read in a
program. The program currently looks like this:
ifstream file;
file.open ("file");
e=0;
while (file.good()) {
getline ( file, infor,',');
istringstream (infor) >> infoc;
var1[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var2[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var3[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var4[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var5[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var6[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var7[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var8[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var9[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var10[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var11[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var12[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var13[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var14[e]=infoc;
getline ( file, infor,',');
istringstream (infor) >> infoc;
var15[e]=infoc;
++e;
}
var1[e] = var1[e] + v1;
var2[e] = var2[e] + v2;
var3[e] = var3[e] + v3;
var4[e] = var4[e] + v4;
var5[e] = var5[e] + v5;
var6[e] = var6[e] + v6;
var7[e] = var7[e] + v7;
var8[e] = var8[e] + v8;
var9[e] = var9[e] + v9;
var10[e] = var10[e] + v10;
var11[e] = var11[e] + v11;
var12[e] = var12[e] + v12;
var13[e] = var13[e] + v13;
var14[e] = var14[e] + v14;
var15[e] = var15[e] + v15;
//WRITE TO compYTD
file.close();
Before i close the file i want to write the new calculated variables back
to the file, erasing everything that was previously read. Is there a
function that allows me to do this? Also is there a separate function that
allows me to write back to this file, adding on to the lines already
there?