Question

I generated a shared library which wraps MySQL C API functions. It has a sample.h and sample.cpp files like this

using namespace std;
class MysqlInstance
{
    protected:
    string user;
    string password;
    string socket;
    int port;

    public:
    MySqlInstance(string,string,string,port);
    int connectToDB();
 }

In sample.cpp

MySqlInstance::MySqlInstance(string user,string pass,string sock,int port)
{
 this->port=port;
 this->user=user;
 this->password=pass;
 this->socket=sock;
}
MySqlInstance::connectToDB()
{
 //code to load libmysqlclient.so from /usr/lib64 and use mysql_init and mysql_real_connect 
 // functions to connect and "cout" that connection is successful
}

Used:

• g++ -fPIC -c sample.cpp mysql_config --cflags

• g++ -shared -Wl,-soname,libsample.so -o libsample.so sample.o mysql_config --libs

Now libsample.so is generated and I moved it to /usr/lib
Now I created a small cpp file which uses this shared library in the same directory.
usesample.cpp

#include "sample.h"
using namespace std;
int main()
{
 MysqlInstance* object=new MySQlInstance("root","toor","/lib/socket",3306);
}

Used:

• g++ -c usesample.cpp -lsample

It is giving me this error:

error: âMysqlInstanceâ was not declared in this scope
error: object was not declared in this scope

Thanks

Answer 1

You have a few errors. One, is the constructor declaration

 MySqlInstance(string,string,string,port);

You probably mean

MySqlInstance(string,string,string,int);

Then, the definition, you have the type of port wrong:

MySqlInstance::MySqlInstance(string user,string pass,string sock,string port) { .... }
                                                              //   ^ should be int

Then, the class name

class MyqllInstance { .... };

should be

class MySqlInstance { .... };

Then, you are using MySQlInstance in main but your class is MySqlInstance.

Remember, C++ is not case insensitive.

Finally, do not put using namespace std in a header file. In fact, do not put it anywhere.