Precompilers, OCI & OCCI :: Connecting To Oracle Database With Instant Client 11.01.06

connecting to an oracle db with the instant client 11.01.06. I can connect to the db via other tools like sqldbx or SqlTools 1.5 which are also using oci. So now I tried it with c++ using Visual Studio 2005 SP1.

First I tried this

Environment* env=Environment::createEnvironment(Environment::DEFAULT);
Connection* con=NULL;
try{
con=env->createConnection("user","pwd","//servername:ip/mydb");
}

and got following error: "the attribute OCI_ATTR_USERNAME is greater than the maximum allowable length of 255".

So I tried:

Environment* env=Environment::createEnvironment(Environment::DEFAULT);
Connection* con=NULL;
try{
con=env->createConnection("user","pwd","tnsservice-name");
}

where tnsservice-name is the name I specified in the tnsnams.ora, and which I used with the other tools working fine -> same error.My username is only 4 long, so I thought it might have something to do with the string. So I tried:

Environment* env=Environment::createEnvironment(Environment::DEFAULT);
Connection* con=NULL;
string user="user";
string passwd="pwd";
string db="tnsservice-name";
try{
con=env->createConnection(user,passwd,db);
AfxMessageBox("sucess");
}

now it returned the error "TNS:connect descriptor too long". Can't have anything to do with the .ora file, since it worked fine for the other tools. Plus it didn't matter if I renamed the .ora file or removed it from the TNS_ADMIN directory..So I searched a little more for a solution and so an example, where the the last argument is missing. So I tried

string user="user";
string pwd="pwd";
Environment* env=Environment::createEnvironment(Environment::DEFAULT);
Connection* con=NULL;
try{
con=env->createConnection(user,pwd);
}

It returns: "TNS: protocol Adapter error" which I somehow can understand, since the adapter doesn't know to wich db to connect.I also tried to use some frameworks like soci or otl but was never able to compile them... (link errors, unknown data types etc...).