C ++链接器问题与静态方法 [英] C++ linker problems with static method
问题描述
我在写一个Vector3D类,在VectorMath类上调用静态方法来执行计算。当我编译时,我得到这个:
I'm writing a Vector3D class that calls a static method on a VectorMath class to perform a calculation. When I compile, I get this:
bash-3.1$ g++ VectorMath.cpp Vector3D.cpp
/tmp/cc5cAPia.o: In function `main':
Vector3D.cpp:(.text+0x4f7): undefined reference to 'VectorMath::norm(Vector3D*)'
collect2: ld returned 1 exit status
代码:
VectorMath.h: p>
VectorMath.h:
#ifndef VECTOR3D_H
#include "Vector3D.h"
#endif
class VectorMath {
public:
static Vector3D* calculatePerpendicularVector(Vector3D*, Vector3D*);
static Vector3D* norm(Vector3D*);
static double length(Vector3D*);
};
VectorMath.cpp
#include "VectorMath.h"
Vector3D* norm(Vector3D* vector) { // can't be found by linker
// do vector calculations
return new Vector3D(xHead, yHead, zHead, xTail, yTail, zTail);
}
// other methods
Vector3D.cpp < b>
Vector3D.cpp
#include "Vector3D.h"
#include "VectorMath.h"
// ...
// vector implementation
// ...
int main(void) {
Vector3D* v = new Vector3D(x, y, z);
Vector3D* normVector = VectorMath::norm(v); // error here
}
为什么链接器找不到 VectorMath :: norm
方法?乍一看,我认为我需要像这样声明规范:
Why can't the linker find the VectorMath::norm
method? At first glance I'd think that I'd need to declare norm like this:
Vector3D* VectorMath::norm(Vector3D* vector) {
但这不能帮助...
推荐答案
您错过了这一点:
//VectorMath.cpp
#include "VectorMath.h"
|
V - here
Vector3D* VectorMath::norm(Vector3D* vector)
{
...
}
norm
函数是 VectorMath ::
。没有它,你只有一个自由的功能。
The norm
function is part of VectorMath::
. Without that, you just have a free function.
,但为什么你使用指针的一切?这更干净:
This is more about your design, but why are you using pointers to everything? This is much cleaner:
class VectorMath {
public:
static Vector3D norm(const Vector3D&);
};
参考,你是C ++,所以不要写C代码。当我调用这个时会发生什么?
Take references, you're in C++ so don't write C code. What happens when I call this?
VectorMath::norm(0); // null
它会崩溃,你必须放入支票,在这种情况下,什么应该返回吗?
It will either crash, you have to put in a check, in which case, what should it return? This is all cleaned up by using references.
此外,为什么不让这些 Vector3D
类的成员?
Also, why not just make these members of the Vector3D
class?
Vector3D* v = new Vector3D(x, y, z);
v->norm(); // normalize would be better, in my opinion
最后,堆栈分配的东西。您的代码现在有内存泄漏:
Lastly, stack-allocate things. Your code right now has a memory leak:
int main(void) {
Vector3D* v = new Vector3D(x, y, z);
Vector3D* normVector = VectorMath::norm(v);
// delete v;
// ^ you're not deleting it!
}
将其更改为此,并使用RAII 概念:
Change it to this, and use RAII concepts:
int main(void) {
Vector3D v(x, y, z);
Vector3D* normVector = VectorMath::norm(v);
// delete v;
// ^ you're not deleting it!
}
通过 norm
一个成员函数,你最终得到的代码非常干净:
And by making norm
a member function you end up with the very clean code:
int main(void) {
Vector3D v(x, y, z);
Vector3D normVector(v.norm());
}
没有指针,没有泄漏,所有性感。
No pointers, no leaks, all sexy.
这篇关于C ++链接器问题与静态方法的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!