Ending a function

Question

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);
			 //this sets the size for the window
			 glutInitWindowSize(800, 700);
			 //create the window with a title
			 glutCreateWindow("This is a window title");
			 //this is the method that will have all the draw stuff.	
			 glutDisplayFunc(display);
			 glutIdleFunc(display);
			 glutMainLoop();
			 return 0;
		 }
Strange, have been using the above functions, was told that the reason that the first function "display" does not work is because I have the semi colon after the (void). When I remove, get an error at the first "{" after the (void)? The second function also has the ";" after the function glutInit and it loads properly, without error. In any event, when I leave the ";" after each function, loads properly but get a linker error that states that the "display" function not found, very strange indeed, any help appreciated, Sid Kraft

Answer 1

Hello @Sid Kraft ,

It appears the semicolon after void display(void); turns it into a function declaration rather than a definition, which likely causes the linker error. Removing the semicolon is the expected approach. If you see an error at { after removing it, this suggests there might be another syntax issue slightly earlier in your file.

Additionally, glutInit is a built-in library function meant to be called, not redefined. It might be beneficial to move your window initialization code and the return 0; statement into a standard int main(int argc, char** argv) function.

Below is a structure you could try:

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;
}

Let me know if this helps resolve the build issues. If you found my response helpful or informative, I would greatly appreciate it if you could follow this guide for your confirmation.

Thank you.

Answer 2

Had you simply followed the answers given at

https://learn.microsoft.com/en-us/answers/questions/5962084/opengl-still

and

https://learn.microsoft.com/en-us/answers/questions/5961746/opengl-glutinit

the problem with the display function would have been resolved.

Answer 3

The problem is the semicolon after the function declaration.

In C++, this:

void display(void);
{
    ...
}

means:

• void display(void); is only a declaration.
• The following { ... } is just a separate block, not the body of display.

That explains the linker error: display was declared, but never actually defined.

The same issue exists for the other function. A function definition must not have a semicolon before its body.

Also, glutInit is a GLUT library function, not a function to redefine. The code shown appears to be intended as main, because it ends with return 0;.

Use this structure instead:

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;
}

Key points:

• Remove the ; after void display(void) when defining the function.
• Do not define glutInit as a function. Call it from main.
• return 0; belongs in main, not in a void function.

If removing the semicolon causes an error at {, that usually means there is another syntax problem nearby, but the semicolon itself is definitely wrong for a function definition.

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