error LNK2019: unresolved external symbol __imp__debugf referenced in function "int __cdecl fld_new - visual-c++

Question

I am upgrading my project from VS 6 to VS 2010, while building in release mode, I am facing the below error.
1>Creating library .\Release\JfFrpF32.lib and object .\Release\JfFrpF32.exp>
1>FLD_.obj : error LNK2019: unresolved external symbol __imp__debugf referenced in function "int __cdecl fld_new(char *,unsigned char,unsigned char,short,char,char,unsigned char,short,char,double,double,short,char *,char,short,short)" (?fld_new##YAHPADEEFDDEFDNNF0DFF#Z)
1>Release/JfFrpF32.dll : fatal error LNK1120: 1 unresolved externals
1>
1>Build FAILED.
Please help me .. thanks in advance..

Answer 1

Common problems that cause LNK2019 include:
The declaration of the symbol contains a spelling mistake, such that,
it is not the same name as the definition of the symbol.
A function was used but the type or number of the parameters did not
match the function definition.
The calling convention (__cdecl, __stdcall, or __fastcall) differs on
the use of the function declaration and the function definition.
Symbol definitions are in a file that was compiled as a C program and
symbols are declared in a C++ file without an extern "C" modifier. In
that case, modify the declaration.
For More Information See Here

Answer 2

In my case, even though I used extern "C", I got the unresolved symbol error.
The hpp was
extern "C"
{
class A
{
public:
void hi();
};
A* a;
DECLDIR int Connect();
}//extern
and the cpp was
#include "DatabasePlugin.hpp"// Include our header, must come after #define DLL_EXPORT
extern "C" // Get rid of name mangling
{
DECLDIR int Connect()
{
a = new A();
a->hi();
return 0;
}//Connect
}//extern
The problem was that I had not created an implementation for the hi() function. Adding it solved the problem. Like this:
extern "C" // Get rid of name mangling
{
void A::hi() {}
DECLDIR int Connect()
{
a = new A();
a->hi();
return 0;
}//Connect
}//extern
Having to declare Hi() before Connect() may also be significant.