Question

while i want to compile my opengl code i get the following errors:

Error   1   error LNK2019: unresolved external symbol __imp__glewInit@0 
Error   2   error LNK2019: unresolved external symbol __imp__glewGetErrorString@4 
Error   3   error LNK2001: unresolved external symbol __imp____glewAttachShader     
Error   4   error LNK2001: unresolved external symbol __imp____glewCompileShader    
Error   5   error LNK2001: unresolved external symbol __imp____glewCreateProgram    
Error   6   error LNK2001: unresolved external symbol __imp____glewCreateShader 
Error   7   error LNK2001: unresolved external symbol __imp____glewDeleteProgram    
Error   8   error LNK2001: unresolved external symbol __imp____glewDisableVertexAttribArray 
Error   9   error LNK2001: unresolved external symbol __imp____glewEnableVertexAttribArray  
Error   10  error LNK2001: unresolved external symbol __imp____glewGetAttribLocation    
Error   11  error LNK2001: unresolved external symbol __imp____glewGetProgramiv 
Error   12  error LNK2001: unresolved external symbol __imp____glewGetShaderiv  
Error   13  error LNK2001: unresolved external symbol __imp____glewLinkProgram  
Error   16  error LNK2001: unresolved external symbol __imp____glewVertexAttribPointer  
Error   17  error LNK1120: 16 unresolved externals  

my code is :

#include <Windows.h>
#include <iostream>
#include <glew.h>
#include <gl\GL.h>
#include <freeglut.h>

using namespace std;

GLuint program;
GLint attribute_coord2d;

int init_resources(void)
{
  GLint compile_ok = GL_FALSE, link_ok = GL_FALSE;

  GLuint vs = glCreateShader(GL_VERTEX_SHADER);
  const char *vs_source = 
#ifdef GL_ES_VERSION_2_0
    "#version 100\n"  // OpenGL ES 2.0
#else 
    "#version 120\n"  // OpenGL 2.1
#endif
    "attribute vec2 coord2d;                  "
    "void main(void) {                        "
    "  gl_Position = vec4(coord2d, 0.0, 1.0); "
    "}";
  glShaderSource(vs, 1, &vs_source, NULL);
  glCompileShader(vs);
  glGetShaderiv(vs, GL_COMPILE_STATUS, &compile_ok);
  if (0 == compile_ok)
  {
    fprintf(stderr, "Error in vertex shader\n");
    return 0;
  }

   GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
  const char *fs_source =
    "#version 120           \n"
    "void main(void) {        "
    "  gl_FragColor[0] = 0.0; "
    "  gl_FragColor[1] = 0.0; "
    "  gl_FragColor[2] = 1.0; "
    "}";
  glShaderSource(fs, 1, &fs_source, NULL);
  glCompileShader(fs);
  glGetShaderiv(fs, GL_COMPILE_STATUS, &compile_ok);
  if (!compile_ok) {
    fprintf(stderr, "Error in fragment shader\n");
    return 0;
  }

   program = glCreateProgram();
  glAttachShader(program, vs);
  glAttachShader(program, fs);
  glLinkProgram(program);
  glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
  if (!link_ok) {
    fprintf(stderr, "glLinkProgram:");
    return 0;
  }

    const char* attribute_name = "coord2d";
  attribute_coord2d = glGetAttribLocation(program, attribute_name);
  if (attribute_coord2d == -1) {
    fprintf(stderr, "Could not bind attribute %s\n", attribute_name);
    return 0;
  }

  return 1;
}

void onDisplay()
{
  /* Clear the background as white */
  glClearColor(1.0, 1.0, 1.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);

  glUseProgram(program);
  glEnableVertexAttribArray(attribute_coord2d);
  GLfloat triangle_vertices[] = {
     0.0,  0.8,
    -0.8, -0.8,
     0.8, -0.8,
  };
  /* Describe our vertices array to OpenGL (it can't guess its format automatically) */
  glVertexAttribPointer(
    attribute_coord2d, // attribute
    2,                 // number of elements per vertex, here (x,y)
    GL_FLOAT,          // the type of each element
    GL_FALSE,          // take our values as-is
    0,                 // no extra data between each position
    triangle_vertices  // pointer to the C array
  );

  /* Push each element in buffer_vertices to the vertex shader */
  glDrawArrays(GL_TRIANGLES, 0, 3);
  glDisableVertexAttribArray(attribute_coord2d);
 
  /* Display the result */
  glutSwapBuffers();
}

void free_resources()
{
  glDeleteProgram(program);
}


int main(int argc, char* argv[])
{
  /* Glut-related initialising functions */
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGBA|GLUT_DOUBLE|GLUT_DEPTH);
  glutInitWindowSize(640, 480);
  glutCreateWindow("My First Triangle");

  /* Extension wrangler initialising */
  GLenum glew_status = glewInit();
  if (glew_status != GLEW_OK)
  {
    fprintf(stderr, "Error: %s\n", glewGetErrorString(glew_status));
    return EXIT_FAILURE;
  }

  /* When all init functions runs without errors,
  the program can initialise the resources */
  if (1 == init_resources())
  {
    /* We can display it if everything goes OK */
    glutDisplayFunc(onDisplay);
    glutMainLoop();
  }

  /* If the program exits in the usual way,
  free resources and exit with a success */
  free_resources();
  return EXIT_SUCCESS;
}

i tried every thing from tweaking linker option including .lib files explicitly, specifying include paths reading forums related to these errors and so on, none of them helped, can you guys help me how i fix this problem?

Answer 1

I got the glew binaries from http://glew.sourceforge.net/index.html (https://sourceforge.net/projects/glew/files/glew/1.9.0/glew-1.9.0-win32.zip/download)
and freeglut 2.8.0 MSVC Package from http://www.transmissionzero.co.uk/software/freeglut-devel/ (http://files.transmissionzero.co.uk/software/development/GLUT/freeglut-MSVC.zip)

I set the include path to glew-1.9.0\include\, freeglut\include\ and library path to freeglut\lib\, glew-1.9.0\lib\.

I corrected the header of your file as

#include <Windows.h>
#include <iostream>
#include <gl/glew.h>
#include <gl/GL.h>
#include <gl/freeglut.h>

#pragma comment(lib, "glew32.lib")

Linking successful, and it worked.

UPD

When using third-party libraries, usually:

• You must set the include path to <3rdPartyDir>\include, but not to <3rdPartyDir>\include\lib_name. Declare its inclusion in the source code should be:

correct: #include <lib_name/header_name.h>

wrong: #include <header_name.h>, because within the library can be internal dependencies, for example #include <lib_name/other_header_name.h>

• Set the library path to <3rdPartyDir>\lib. Then, you must specify the required libraries, one of the following methods:

For MSVC, add

#ifdef _MSC_VER
#pragma comment(lib, "lib1_name.lib")
#pragma comment(lib, "lib2_name.lib")
/// etc
#endif

Or, add the required libraries to the linker options.

Some libraries support auto-linking mechanism (for example, freeglut), that is, the header file contains a line like #pragma comment(lib, "lib1_name.lib")

• Copy the required dlls from <3rdPartyDir>\bin to <MyExePath>\