"unresolved external symbol _triangulate" when using triangle library - c++

Question

I'm currently using the triangle library in my program. The library contains only .c and .h files (no .lib). I get the following error on Visual Studio C++ 2010:
1>data.obj : error LNK2019: unresolved external symbol _triangulate referenced in function "struct triangulateio __cdecl readfile(void)" (?readfile##YA?AUtriangulateio##XZ)
The header file of my data.cpp is the following:
#ifndef DATA_H
#define DATA_H
#include <WinSock2.h>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <fstream>
#include <string>
#include <time.h>
#include <GL/gl.h> //include the gl header file
#include <GL/glut.h> //include the glut header file
#include <GL/glu.h> //include the glut header file
#include <armadillo>
//Namespace
using namespace std;
using namespace arma;
extern "C"
{
#ifdef SINGLE
#define REAL float
#else /* not SINGLE */
#define REAL double
#endif /* not SINGLE */
#include "triangle.h"
}
triangulateio readfile();
#endif
Data.cpp
triangulate("pczAevn", &in, &mid, &vorout);
I've already made my program work with a Makefile of mine on Ubuntu, but I need to run my program on windows.
Feel free to ask for more information.
EDIT #1:
If you use the triangle library with VS, you have to put the following instruction on top of the triangle.c file #define TRILIBRARY
Now it compile. Thank you very much for the help.

Answer 1

The linker can't find a definition for "triangulateio readfile()", if it's defined in the .c file my guess is that it isn't built. If you include it in the project it could work.