Already has a body

Question

//OpenGL functions, open a window and initialize
void display(void)
{
	glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();
	glFlush();
}
void glutInit(int* argcp, char** argv)
{
	glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH);
	glutInitWindowPosition(100, 200);
	glutInitWindowSize(800, 700);
	glutCreateWindow("This is a window title");
	glutDisplayFunc(display);
	glutIdleFunc(display);
	glutMainLoop();
}
int main()
Finally resolved the problem above by placing the display and glutInit functions outside of the main function, then executed ok. However, now getting an error C2084 says the glutInit function already has a body? Not sure what this means and why, please advise, Sid Kraft

Answer 1

C/C++ does not allow methods to be defined inside another method. but C++ has support for lambda, which are used to define anonymous functions with closure. you can declare a variable and define as a lambda inside a method.

note: like fortran, C/C++ does not support calling a method that was not defined earlier in the source file. to get around this you use a forward declaration (function prototype). so the sample code could be written:

void initWindow(int* argc, char** argv);
void display(void);

int main(int argc, char** argv)
{
    initWindow(&argc, argv);
    glutMainLoop();
    return 0;
}

void initWindow(int* argc, char** argv)
{
    glutInit(argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH);
    glutInitWindowPosition(100, 200);
    glutInitWindowSize(800, 700);
    glutCreateWindow("This is a window title");
    glutDisplayFunc(display);
    glutIdleFunc(display);
}

void display(void)
{
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glFlush();
}

Answer 2

C2084 means a function was defined more than once.

In this code, the problem is the function name glutInit:

void glutInit(int* argcp, char** argv)

glutInit is already provided by the GLUT library, so writing a function with that same signature creates a second definition. The compiler reports that the function already has a body.

Use a different name for the function that sets up the window, for example:

void display(void)
{
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glFlush();
}

void initWindow(int* argc, char** argv)
{
    glutInit(argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH);
    glutInitWindowPosition(100, 200);
    glutInitWindowSize(800, 700);
    glutCreateWindow("This is a window title");
    glutDisplayFunc(display);
    glutIdleFunc(display);
}

int main(int argc, char** argv)
{
    initWindow(&argc, argv);
    glutMainLoop();
    return 0;
}

Also make sure the needed OpenGL headers are included:

• Core OpenGL: <GL\gl.h>
• GLU: <GL\glu.h>
• WGL and Windows support: Windows.h

---

References:

• Compiler Error C2084
• Header Files

Answer 3

Hi @Sid Kraft .

I see the issue is an active compiler error C2084 stating that glutInit already has a body.

The error C2084 means that a function has been defined more than once. glutInit is already a built-in function provided by the OpenGL GLUT utility library. When you define void glutInit(int* argcp, char** argv) in your code, the compiler stops you because it sees two definitions for the exact same function.

To resolve this, you shouldn't create a custom function named glutInit. Instead, you should simply call the library's glutInit from within your main function (or create a custom function with a different name, like setupOpenGL) to initialize the window, like this:

void display(void)
{
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glFlush();
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH);
    glutInitWindowPosition(100, 200);
    glutInitWindowSize(800, 700);
    glutCreateWindow("This is a window title");
    glutDisplayFunc(display);
    glutIdleFunc(display);
    glutMainLoop();
    return 0;
}

If you found my response helpful or informative, I would greatly appreciate it if you could follow this guidance or provide feedback.

Let me know if you need anything else.

Thank you.