GLSL loading core dumped - opengl

Question

I am compiling this project on a linux machine. After fixing all the include and lib errors, I get a core dumped error. but if I comment out the initGLSL line, it runs well. The initGLSL function is given below.
void Viewer :: initGLSL( void )
{
shader.loadVertex( "shaders/vertex.glsl" );
shader.loadFragment( "shaders/fragment.glsl" );
}
vertex.glsl:
varying vec3 position;
varying vec3 normal;
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
gl_FrontColor = gl_Color;
position = gl_Vertex.xyz;
normal = gl_Normal.xyz;
}
I don't know how to debug this program. How can I check if this error is because of the GLSL, or the loader function?
---------------Thanks for your comment------------
The load function:
void Shader::loadVertex( const char* filename )
{
load( GL_VERTEX_SHADER, filename, vertexShader );
}
void Shader::loadFragment( const char* filename )
{
load( GL_FRAGMENT_SHADER, filename, fragmentShader );
}
void Shader::load( GLenum shaderType, const char* filename, GLuint& shader )
// read vertex shader from GLSL source file, compile, and attach to program
{
string source;
if( !readSource( filename, source ))
{
return;
}
if( program == 0 )
{
program = glCreateProgram();
}
if( shader != 0 )
{
glDetachShader( program, shader );
}
shader = glCreateShader( shaderType );
const char* source_c_str = source.c_str();
glShaderSource( shader, 1, &(source_c_str), NULL );
glCompileShader( shader );
GLint compileStatus;
glGetShaderiv( shader, GL_COMPILE_STATUS, &compileStatus );
if( compileStatus == GL_TRUE )
{
glAttachShader( program, shader );
linked = false;
}
else
{
GLsizei maxLength = 0;
glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &maxLength );
if( maxLength > 0 )
{
GLchar* infoLog = new char[ maxLength ];
GLsizei length;
glGetShaderInfoLog( shader, maxLength, &length, infoLog );
cerr << "GLSL Error: " << infoLog << endl;
delete[] infoLog;
}
}
}
and when I tried debugging with gdb, I get the msg:
(gdb) p (filename)
$1 = 0x482e41 "shaders/vertex.glsl"
(gdb) n
77 if( program == 0 )
(gdb) n
79 program = glCreateProgram();
(gdb) n
Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()

Answer 1

Have you definitely created an OpenGL context before calling shader.load*?
E.g. one of these, if you're using the corresponding library:
glutInit
glutCreateWindow
glfwInit
glfwCreateWindow
SDL_init
SDL_CreateWindow
SDL_GL_CreateContext
I don't have much experience with this, but some GL functions aren't linked at runtime by default - glCreateProgram may still be NULL after creating a context. I use GLEW to do this for me (glewInit()), but there are other ways.