Question

I want to implement a function with OpenGL to render a cylinder in C++. The signature of my function is as follows:

#define POINTS_NUM  15
#define DEMESION    3
    
void drawCylinder( int slices, int segments, GLfloat (&vertices)[ POINTS_NUM ][ DEMESION ] );

I want to use a reference to a two-dimensional array to limit user input, but some strange behavior is happening. When I implement the function declared as above, an linker error occurs:

Error 1 error LNK2005: "float (* vase)[3]" (?vase@@3PAY02MA) already defined in shapes.obj vase.obj VaseAndAnimation

Here vase is defined as:

GLfloat vase[ POINTS_NUM ][ DEMESION ];

At first, I thought there was something wrong with the last dimension. So I omitted it in my second trial. This time declaration of my function is like this:

void drawCylinder( int slices, int segments, GLfloat (&vertices)[ POINTS_NUM ][] );

Now a compile-time error occurs when invoked as (vase definition isn’t changed):

drawCylinder( 10, 10, vase );

Compile error:

Error 1 error C2087: ‘vertices’ : missing subscript d:\visual studio 2008\projects\project1\computer graphics\vaseandanimation\shapes.h 25 VaseAndAnimation

Error 2 error C2664: ‘drawCylinder’ : cannot convert parameter 3 from ‘GLfloat [14][3]’ to ‘GLfloat (&)[14][1]’ d:\Visual Studio 2008\Projects\Project1\Computer Graphics\VaseAndAnimation\vase.cpp 64 VaseAndAnimation

Error 3 error C2087: ‘vertices’ : missing subscript d:\visual studio 2008\projects\project1\computer graphics\vaseandanimation\shapes.h 25 VaseAndAnimation

Error 4 error C2087: ‘vertices’ : missing subscript d:\Visual Studio 2008\Projects\Project1\Computer Graphics\VaseAndAnimation\shapes.cpp 12 VaseAndAnimation

From this error, I can see that parameter vertices is really treated a reference to a two-dimensional array, but why is vase parsed as float (* vase)[3] in my first version?

My IDE is Visual Studio 2008. I haven’t tried it with GCC; is that behavior compiler-dependent?

Hope someone can give me a hand to get rid of the trap.

Answer 1

Your first declaration is fine. Seems to be you have defined vase in a header file.