c++ - Can we hide unimportant declarations in Header files? -

i decided export of functions static library (.lib). decided not give complete header files users. kept private , protected variables , methods out of it, end-users should not use them , should not have include other headers class declarations.

unexpectedly ran heap-corruption errors when creating instances of classes exported static lib.

this original header file:

// original header file class codbchelper { public:     codbchelper();     virtual ~codbchelper();  public:     std::vector<userdata> getuserinformation();  private:     sqlhenv     m_henv;     sqlhdbc     m_hdbc;     sqlhstmt    m_hstmt; }; 

then decided take private variables out, users of .lib not abuse them , not have include unnecessary sql header files:

// minimized header file class codbchelper { public:     codbchelper();     virtual ~codbchelper();  public:     std::vector<userdata> getuserinformation(); }; 

i noticed sizeof operation returns different values depending called.

called in .lib:

int size = sizeof(codbchelper); // size 12 

called in linking project:

int size = sizeof(codbchelper); // size 1 

doing following code in linking project causes heap corruption (which happens because of wrong size calculations):

codbchelper* helper = new codbchelper; 

doing like

class codbchelper { [...] private:     char padding[12]; } 

would solve problem, think bad behavior , not maintainable @ all.

so there way tell compiler how big real object (from linked library) going be? or there easy way of hiding declarations in header files not needed users?

i don't see how "hiding unimportant members" connected removing them class definition.

i guess, wanted eliminate unnecessary dependencies code. technique - reduces compilation time, makes code more portable between different versions , more.

the thing is, changed class completely. if designed have 3 private members:

sqlhenv     m_henv; sqlhdbc     m_hdbc; sqlhstmt    m_hstmt; 

you cannot remove them. not "hiding implementation details" means.

or there easy way of hiding declarations in header files not needed users?

what want use pimpl idiom:

//minimized header file class codbchelper { public:     codbchelper();     virtual ~codbchelper();  public:     std::vector<userdata> getuserinformation();  private:     struct internaldata;     internaldata* m_internal_data; }; 

then, in .cpp file:

struct codbchelper::internaldata {     sqlhenv     m_henv;     sqlhdbc     m_hdbc;     sqlhstmt    m_hstmt; }; 

now change implementation use m_internal_data instead of each component separately. profitable if software updated - forbids clients create code, depends on implementation details of types.

you may want read point 2. and/or 4. of this answer.