Symbol(s) not found for architecture x86_64 (OpenGL with xcode) - c++

Question

I am very new to using OpenGL. The program I am trying to run is provided by my professor so I have not actually written any of it, I am having problems getting the program to run. The program is suppose to just make a white square on a black screen. I am using mac Sierra 10.12.2. Also I have already changed the deployment target to 10.8 because of the errors from compiling in anything later than that. Now when I try to build and run in xcode I get 2 errors.
These are the errors im getting,
Undefined symbols for architecture x86_64:
"exit(int)", referenced from:
myKeyboard(unsigned char, int, int) in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Now here is the code exactly as I am trying to compile it.
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#include <OpenGL/OpenGL.h>
#include <GLUT/glut.h>
const int screenHeight = 480; // window height is 480
const int screenWidth = 640 ; //window width is 640
// <<<<<<<<<<<<<<<<<<<<< Prototypes >>>>>>>>>>>>>>>>>>
void exit(int) ;
// <<<<<<<<<<<<<<<<<<<<<<< myInit >>>>>>>>>>>>>>>>>>>
void myInit(void)
{
glClearColor(1.0,1.0,1.0,0.0); // set white background color
glColor3f(0.0f, 0.0f, 0.0f); // set the drawing color
glPointSize(4.0); // a ?dot? is 4 by 4 pixels
glLineWidth(4.0); // a ?dot? is 4 by 4 pixels
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, 640.0, 0.0, 480.0);
}
// <<<<<<<<<<<<<<<<<<<<<<<< myDisplay >>>>>>>>>>>>>>>>>
void myDisplay(void)
{
glClear(GL_COLOR_BUFFER_BIT); // clear the screen
glBegin(GL_POINTS);
// glBegin(GL_LINE_STRIP) ;
// glBegin(GL_LINE_LOOP) ;
// glBegin(GL_POLYGON);
glVertex2i(289, 190); // Dubhe
glVertex2i(320, 128) ; // Merak
glVertex2i(239, 67) ; // Phecda
glVertex2i(194, 101) ; // Megrez
glVertex2i(129, 83) ; // Alioth
glVertex2i(75, 73) ; // Mizar
glVertex2i(74, 74) ; // Alcor
glEnd();
glFlush(); // send all output to display
}
// <<<<<<<<<<<<<<<<<<<<<<<< myKeyboard >>>>>>>>>>>>>>
void myKeyboard(unsigned char theKey, int mouseX, int mouseY)
{
switch(theKey)
{
case 'Q':
case 'q':
exit(-1); //terminate the program
default:
break; // do nothing
}
}
// <<<<<<<<<<<<<<<<<<<<<<<< main >>>>>>>>>>>>>>>>>>>>>>
int main(int argc, char** argv)
{
glutInit(&argc, argv); // initialize the toolkit
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // set display mode
glutInitWindowSize(640, 480); // set window size
glutInitWindowPosition(100, 150); // set window position on screen
glutCreateWindow("Big Deep - Type Q or q to quit") ; // open the screen window
glutDisplayFunc(myDisplay); // register redraw function
glutKeyboardFunc(myKeyboard); // register the keyboard action function
myInit();
glutMainLoop(); // go into a perpetual loop
}
Any help would be greatly appreciated!

Answer 1

You need to add the following near the top of your source file:
#include <stdlib.h>
and remove this line:
void exit(int) ;
First, you should always use the proper system headers to get the declarations of system library functions. This is especially true on macOS where the declaration can have important attributes which affect how the function is linked.
However, the lack of such attributes is not really what tripped you up in this case. The issue here is that you're building a C++ program. In C++, a function's argument types are part of its symbol name. You can see this in the error message you've quoted. But the exit() function is part of the C standard library. It's not natively a C++ interface. Its symbol name is _exit, with no indication of its argument count or types.
Your code has incorporated references to a symbol that translates to exit(int) while the actual symbol in the system library is just _exit. They don't match, so you get a symbol-not-found linker error.
The stdlib.h header takes special care to wrap its function declarations in extern "C" { ... } when it's included for a C++ translation unit. So, including that header to get the declaration tells the C++ compiler not to use a C++-style symbol name but to instead just use the C-style symbol name.
You could also "solve" the issue by putting extern "C" on the declaration of exit() in your own code, but that's the wrong approach. Just include the proper header.