Problem in creating dll

[tonyaim83]

Hi
My current editor is Dev-Cpp 4.9.2.2 .My test program which runs fine looks like
dll.h

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

#ifdef __cplusplus
extern "C"
{
 #endif
  __declspec(dllexport) void HelloWorld();
#ifdef __cplusplus
}
#endif

And dll.cpp

#include"dll.h"

void HelloWorld ()
{
    MessageBox (0, "This is a sample application!\n", "Hi", MB_ICONINFORMATION);
}

This code runs fine. Now i tried the same thing with my program where i'm using boostlib.
so my dll.h changed to

/*List of header files */

using namespace boost;
using namespace std;    
   
//Contains vertex properties of a graph
struct Vertex_Prop 
{
    string name;
 };

//Contains edge properties of a graph
struct Edge_Prop
{
    int weight;
 };           

typedef graph_traits <adjacency_list<> >::vertex_descriptor Vertex;
struct Graph_Prop
{
   std::map<string,Vertex> nodes;
};

typedef adjacency_list <setS, vecS, bidirectionalS, Vertex_Prop, \
        Edge_Prop,Graph_Prop > Graph;

[B]#ifdef __cplusplus
extern "C"
{
  #endif
    __declspec(dllexport) int CreateGraph(Graph &g);
#ifdef __cplusplus
}
#endif
[/B]

This code gives a linking error. Even if you are not well versed with boost i just want to know what is the correct way to write code for bold part if i want to create a dll of this. The above code is running fine when i have created exe or a console application for this. Where in the header i have simply declared the function without any __declspec(dllexport).
Kindly help

[Ancient Dragon]

There is no "bold part". Please refer to the line numbers of the code you posted.

The way I create and use DLLs is to use a macro to determine whether to use __dllimport or __dllexport

#ifdef MYDLL
#define MYAPI __declspec(__dllexport)
#else
#define MYAPI __declspec(__dllexport)
#endif

MYAPI void HelloWorld();

If you put the above in the .h file you can include it in both the DLL and application project. In the DLL project just declare MYDLL

[tonyaim83]

The bold part i'm talking about is from line no. 27-35 the solution provided in which macros need to be defined in the .h files can i remove the extern C as well.

[Ancient Dragon]

>>can i remove the extern C as well.
No, leave that as it is since you want to use the DLL with C code. If you're going to only use it with C++ then you don't need it.