Error "Expected specifier-qualifier-list before" at struct constructor - iphone

Question

I am trying to write some code to optimize some Open GL functions for a program I'm writing, unfortunately, I am not exactly a C or C++ veteran, but that's partially why I'm doing this project!
So I'm creating a struct to handle 3x3 matrices and I am defining the struct as follows:
#ifndef MATRIX3BY3_H
#define MATRIX3BY3_H
struct Matrix3by3
{
float ix, jx, kx;
float iy, jy, ky;
float iz, jz, kz;
Matrix3by3() {}
Matrix3by3(const Matrix3by3 &matrix)
{
ix = matrix.ix;
jx = matrix.jx;
kx = matrix.kx;
iy = matrix.iy;
jy = matrix.jy;
ky = matrix.ky;
iz = matrix.iz;
jz = matrix.jz;
kz = matrix.kz;
}
Matrix3by3 (const float _ix, const float _jx, const float _kx,
const float _iy, const float _jy, const float _ky,
const float _iz, const float _jz, const float _kz) :
ix(_ix), jx(_jx), kx(_kx),
iy(_iy), jy(_jy), ky(_ky),
iy(_iz), jx(_jz), kz(_kz) {}
};
#endif
And I get the error (twice)
Expected specifier-qualifier-list
before 'Matrix3by3'
On the line of the first constructor. I have tried to look around for answers for this, and it seems that it has to do with the compiler not knowing that this is a type. So I have tried the following, I'll remove the innards for brevity:
typedef struct Matrix3by3 { ... };
struct Matrix3by3 { struct Matrix3by3() {} ... };
struct Matrix3by3 { ... } Matrix3by3;
typdef struct Matrix3by3;
struct Matrix3by3 { ... };
Which are all solutions that were suggested on blogs and articles that I saw for this error. I also saw that it may arise because of a circular dependency, but this file has no includes that include anything else, and I've even removed them just to be certain from time to time - no change.
I could write this in a objective-c class, I'm sure, but it will probably take a tiny bit more memory and cycles, and that's exactly what I'm trying to avoid. The only thing I can think of left is some compiler/project setting that I have set by default that precludes my using this type of structure. Entirely possible, as I'm learning the language/environment.
Can any one provide some help?
Thanks!

Answer 1

C does not support constructors or member functions of structs. There is no way you will get this to compile as C or Objective-C. You need to compile this as C++ or Objective-C++, at which point it will almost compile: you have an error in your 3rd constructor, in that you're attempting to initialize the members iy and jx multiple times. Once you fix those typos, it compiles just fine.

Answer 2

typedef struct { ... } Matrix3by3;
should work. It declares the anonymous struct as a type.
And use class instead of struct :)

Answer 3

What language/compiler are you translating your program with? I'd guess that you are trying to compile the code as C, while the language features you are trying to use are strictly C++-specific.

Answer 4

The error "Expected specifier-qualifier-list before 'Matrix3by3'" is a GCC-ism and it means that the token "Matrix3by3" is unknown. This is typically the case when you have a type that the compiler doesn't recognize, either because you mistyped it or because you forgot a header. In your case, it's because the type "Matrix3by3" really doesn't exist. You have two options:
Stop using Matrix3by3 directly and start using struct Matrix3by3 instead, as that's the actual type you defined.
Give your struct a typedef. It will look something like
typedef struct {
// fields here
} Matrix3by3