Build error when trying to run an OpenGL example in VC - visual-studio

Question

What I can''t understand is why the both 2 individual .cpp files compile but the solution does not build. The code that won't compile even though I follow the instructions is
// Two-Dimensional Sierpinski Gasket
// Generated using randomly selected vertices and bisection
#include "Angel.h"
#include <GL/glut.h>
#include <GL/glew.h>
#pragma comment(lib, "glew32.lib")
const int NumPoints = 5000;
//----------------------------------------------------------------------------
void
init( void )
{
vec2 points[NumPoints];
// Specifiy the vertices for a triangle
vec2 vertices[3] = {
vec2( -1.0, -1.0 ), vec2( 0.0, 1.0 ), vec2( 1.0, -1.0 )
};
// Select an arbitrary initial point inside of the triangle
points[0] = vec2( 0.25, 0.50 );
// compute and store N-1 new points
for ( int i = 1; i < NumPoints; ++i ) {
int j = rand() % 3; // pick a vertex at random
// Compute the point halfway between the selected vertex
// and the previous point
points[i] = ( points[i - 1] + vertices[j] ) / 2.0;
}
// Create a vertex array object
GLuint vao;
glGenVertexArrays( 1, &vao );
glBindVertexArray( vao );
// Create and initialize a buffer object
GLuint buffer;
glGenBuffers( 1, &buffer );
glBindBuffer( GL_ARRAY_BUFFER, buffer );
glBufferData( GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW );
// Load shaders and use the resulting shader program
GLuint program = InitShader( "vshader21.glsl", "fshader21.glsl" );
glUseProgram( program );
// Initialize the vertex position attribute from the vertex shader
GLuint loc = glGetAttribLocation( program, "vPosition" );
glEnableVertexAttribArray( loc );
glVertexAttribPointer( loc, 2, GL_FLOAT, GL_FALSE, 0,
BUFFER_OFFSET(0) );
glClearColor( 1.0, 1.0, 1.0, 1.0 ); // white background
}
//----------------------------------------------------------------------------
void
display( void )
{
glClear( GL_COLOR_BUFFER_BIT ); // clear the window
glDrawArrays( GL_POINTS, 0, NumPoints ); // draw the points
glFlush();
}
//----------------------------------------------------------------------------
void
keyboard( unsigned char key, int x, int y )
{
switch ( key ) {
case 033:
exit( EXIT_SUCCESS );
break;
}
}
//----------------------------------------------------------------------------
int
main( int argc, char **argv )
{
glutInit(&argc, argv);
glutInitDisplayMode( GLUT_RGBA );
glutInitWindowSize( 512, 512 );
// If you are using freeglut, the next two lines will check if
// the code is truly 3.2. Otherwise, comment them out
glutInitContextVersion( 3, 1 );
glutInitContextProfile( GLUT_CORE_PROFILE );
glutCreateWindow( "Sierpinski Gasket" );
glewInit();
init();
glutDisplayFunc( display );
glutKeyboardFunc( keyboard );
glutMainLoop();
return 0;
}
I get this strange error message when I try to build the example project from Edward Angel's OpenGL site:
1>------ Build started: Project: 6E test, Configuration: Release Win32 ------
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBindBuffer
1>example1.obj : error LNK2001: unresolved external symbol __imp____glutCreateWindowWithExit#8
1>example1.obj : error LNK2001: unresolved external symbol __imp____glutInitWithExit#12
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewVertexAttribPointer
1>example1.obj : error LNK2001: unresolved external symbol __imp__glewInit#0
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGenVertexArrays
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutInitContextProfile#4
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewUseProgram
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutInitContextVersion#8
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBufferData
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBindVertexArray
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutInitDisplayMode#4
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGetAttribLocation
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGenBuffers
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutKeyboardFunc#4
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutMainLoop#0
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutInitWindowSize#8
1>example1.obj : error LNK2001: unresolved external symbol __imp__glutDisplayFunc#4
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewEnableVertexAttribArray
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCreateShader
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetShaderInfoLog
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewLinkProgram
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCompileShader
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewShaderSource
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetProgramiv
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetShaderiv
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetProgramInfoLog
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCreateProgram
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewAttachShader
1>C:\Users\student\Downloads\6E_example1_VC10\6E test\Release\6E test.exe : fatal error LNK1120: 29 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
It looks to me like I've tried to link in incompatible libraries, what does the above look like to you? The complete source code I try to run (with Windows 7) is
// Two-Dimensional Sierpinski Gasket
// Generated using randomly selected vertices and bisection
#pragma comment(lib, "glew32.lib")
#include "Angel.h"
const int NumPoints = 5000;
//----------------------------------------------------------------------------
void
init( void )
{
vec2 points[NumPoints];
// Specifiy the vertices for a triangle
vec2 vertices[3] = {
vec2( -1.0, -1.0 ), vec2( 0.0, 1.0 ), vec2( 1.0, -1.0 )
};
// Select an arbitrary initial point inside of the triangle
points[0] = vec2( 0.25, 0.50 );
// compute and store N-1 new points
for ( int i = 1; i < NumPoints; ++i ) {
int j = rand() % 3; // pick a vertex at random
// Compute the point halfway between the selected vertex
// and the previous point
points[i] = ( points[i - 1] + vertices[j] ) / 2.0;
}
// Create a vertex array object
GLuint vao;
glGenVertexArrays( 1, &vao );
glBindVertexArray( vao );
// Create and initialize a buffer object
GLuint buffer;
glGenBuffers( 1, &buffer );
glBindBuffer( GL_ARRAY_BUFFER, buffer );
glBufferData( GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW );
// Load shaders and use the resulting shader program
GLuint program = InitShader( "vshader21.glsl", "fshader21.glsl" );
glUseProgram( program );
// Initialize the vertex position attribute from the vertex shader
GLuint loc = glGetAttribLocation( program, "vPosition" );
glEnableVertexAttribArray( loc );
glVertexAttribPointer( loc, 2, GL_FLOAT, GL_FALSE, 0,
BUFFER_OFFSET(0) );
glClearColor( 1.0, 1.0, 1.0, 1.0 ); // white background
}
//----------------------------------------------------------------------------
void
display( void )
{
glClear( GL_COLOR_BUFFER_BIT ); // clear the window
glDrawArrays( GL_POINTS, 0, NumPoints ); // draw the points
glFlush();
}
//----------------------------------------------------------------------------
void
keyboard( unsigned char key, int x, int y )
{
switch ( key ) {
case 033:
exit( EXIT_SUCCESS );
break;
}
}
//----------------------------------------------------------------------------
int
main( int argc, char **argv )
{
glutInit(&argc, argv);
glutInitDisplayMode( GLUT_RGBA );
glutInitWindowSize( 512, 512 );
// If you are using freeglut, the next two lines will check if
// the code is truly 3.2. Otherwise, comment them out
glutInitContextVersion( 3, 1 );
glutInitContextProfile( GLUT_CORE_PROFILE );
glutCreateWindow( "Sierpinski Gasket" );
glewInit();
init();
glutDisplayFunc( display );
glutKeyboardFunc( keyboard );
glutMainLoop();
return 0;
}
#pragma comment(lib, "glew32.lib")
#include "Angel.h"
namespace Angel {
// Create a NULL-terminated string by reading the provided file
static char*
readShaderSource(const char* shaderFile)
{
FILE* fp = fopen(shaderFile, "r");
if ( fp == NULL ) { return NULL; }
fseek(fp, 0L, SEEK_END);
long size = ftell(fp);
fseek(fp, 0L, SEEK_SET);
char* buf = new char[size + 1];
fread(buf, 1, size, fp);
buf[size] = '\0';
fclose(fp);
return buf;
}
// Create a GLSL program object from vertex and fragment shader files
GLuint
InitShader(const char* vShaderFile, const char* fShaderFile)
{
struct Shader {
const char* filename;
GLenum type;
GLchar* source;
} shaders[2] = {
{ vShaderFile, GL_VERTEX_SHADER, NULL },
{ fShaderFile, GL_FRAGMENT_SHADER, NULL }
};
GLuint program = glCreateProgram();
for ( int i = 0; i < 2; ++i ) {
Shader& s = shaders[i];
s.source = readShaderSource( s.filename );
if ( shaders[i].source == NULL ) {
std::cerr << "Failed to read " << s.filename << std::endl;
exit( EXIT_FAILURE );
}
GLuint shader = glCreateShader( s.type );
glShaderSource( shader, 1, (const GLchar**) &s.source, NULL );
glCompileShader( shader );
GLint compiled;
glGetShaderiv( shader, GL_COMPILE_STATUS, &compiled );
if ( !compiled ) {
std::cerr << s.filename << " failed to compile:" << std::endl;
GLint logSize;
glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &logSize );
char* logMsg = new char[logSize];
glGetShaderInfoLog( shader, logSize, NULL, logMsg );
std::cerr << logMsg << std::endl;
delete [] logMsg;
exit( EXIT_FAILURE );
}
delete [] s.source;
glAttachShader( program, shader );
}
/* link and error check */
glLinkProgram(program);
GLint linked;
glGetProgramiv( program, GL_LINK_STATUS, &linked );
if ( !linked ) {
std::cerr << "Shader program failed to link" << std::endl;
GLint logSize;
glGetProgramiv( program, GL_INFO_LOG_LENGTH, &logSize);
char* logMsg = new char[logSize];
glGetProgramInfoLog( program, logSize, NULL, logMsg );
std::cerr << logMsg << std::endl;
delete [] logMsg;
exit( EXIT_FAILURE );
}
/* use program object */
glUseProgram(program);
return program;
}
} // Close namespace Angel block
Update
I changed the code to begin like below and it's still not building and I still get the build error.
#pragma comment(lib, "glew32.lib")
#define GLEW_STATIC 1
#include "Angel.h"
#include <GL\glew.h>
Update 150529
I can build the freeglut GLUT examples so GLUT appears correctly installed with VC, but then when I doubleclick one of the example builds it says that freeglut.dll is not installed on my system. I still get the same compilation error when trying to build Angel's example. Why? What am I doing wrong? What should I do?
1>------ Build started: Project: 6E test, Configuration: Release Win32 ------
1> example1.cpp
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\Angel.h(65): warning C4305: 'initializing' : truncation from 'double' to 'const GLfloat'
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(698): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(699): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(700): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(721): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(723): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(726): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(742): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1> InitShader.cpp
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\Angel.h(65): warning C4305: 'initializing' : truncation from 'double' to 'const GLfloat'
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(698): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(699): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(700): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(721): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(723): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(726): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>c:\users\student\downloads\6e_example1_vc10\6e test\code\mat.h(742): warning C4244: '=' : conversion from 'double' to 'GLfloat', possible loss of data
1>..\CODE\InitShader.cpp(13): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
1> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\stdio.h(218) : see declaration of 'fopen'
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBindBuffer
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewVertexAttribPointer
1>example1.obj : error LNK2001: unresolved external symbol __imp__glewInit#0
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGenVertexArrays
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewUseProgram
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBufferData
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewBindVertexArray
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGetAttribLocation
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewGenBuffers
1>example1.obj : error LNK2001: unresolved external symbol __imp____glewEnableVertexAttribArray
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCreateShader
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetShaderInfoLog
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewLinkProgram
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCompileShader
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewShaderSource
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetProgramiv
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetShaderiv
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewGetProgramInfoLog
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewCreateProgram
1>InitShader.obj : error LNK2001: unresolved external symbol __imp____glewAttachShader
1>C:\Users\student\Downloads\6E_example1_VC10\6E test\Release\6E test.exe : fatal error LNK1120: 20 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Update
I tried asking about this again and it still won't work:
Linker error with glew and Visual Studio on windows 7

Answer 1

You're missing GLEW (The OpenGL Extension Wrangler Library). You can link this in with the following pragma somewhere in your source code:
#pragma comment(lib, "glew32.lib")
Or you can modify the linker flags in the project settings. This assumes that you have the GLEW library installed. On my system, I installed it at the following path:
C:\Program Files (x86)/Microsoft Visual Studio 10.0/VC/lib/glew32.lib
The path may be different on your system, and there are other ways of linking with GLEW if you don't want to install it.

Answer 2

You can let go of GLEW. All it does is to get the GL (and WGL) extensions loaded. Nevertheless you can do it yourself:
1.include the headers (google the file names for download):
#include<GL/glext.h>
#include<GL/wglext.h>
2.declare the function pointers:
PFNGLGENVERTEXARRAYSPROC glGenVertexArrays;
PFNGLBINDVERTEXARRAYPROC glBindVertexArray;
PFNWGLMAKECONTEXTCURRENTARBPROC wglMakeContextCurrentARB;
//etc.
3.load the function pointers via wglGetProcAddress:
glGenVertexArrays = (PFNGLGENVERTEXARRAYSPROC)wglGetProcAddress("glGenVertexArrays");
glBindVertexArray = (PFNGLBINDVERTEXARRAYPROC)wglGetProcAddress("glBindVertexArray");
wglMakeContextCurrentARB = (PFNWGLMAKECONTEXTCURRENTARBPROC)wglGetProcAddress("wglMakeContextCurrentARB");
//etc
4.let the example code use them (no changes)!
glGenVertexArrays( 1, &vao );
//etc