目标c方法中的std :: vector

Question

我在客观的C++中工作.我坚持的问题是我需要将std :: vector传递给目标c方法.这可能吗？下面是我当前的代码,我必须在向量定义方法中对向量进行计算(向数组成员添加偏移值),然后再将该方法作为C数组传递给该方法.理想情况下,我想在第二种方法中设置偏移值,从而拆分定义(将有几个)偏移量将是变量,与下面的示例不同.

因此,我想使用矢量而不是传入(b2Vec2*)vect

- (void)createterrain1 {

using namespace std;
vector<b2Vec2>vecVerts;
vector<int>::size_type i;
vecVerts.push_back(b2Vec2(-1022.5f / 100.0, -20.2f / 100.0));
vecVerts.push_back(b2Vec2(-966.6f / 100.0, -18.0f / 100.0));
vecVerts.push_back(b2Vec2(-893.8f / 100.0, -10.3f / 100.0));
vecVerts.push_back(b2Vec2(-888.8f / 100.0, 1.1f / 100.0));
vecVerts.push_back(b2Vec2(-804.0f / 100.0, 10.3f / 100.0));
vecVerts.push_back(b2Vec2(-799.7f / 100.0, 5.3f / 100.0));
vecVerts.push_back(b2Vec2(-795.5f / 100.0, 8.1f / 100.0));
vecVerts.push_back(b2Vec2(-755.2f/ 100.0, -9.5f / 100.0));
vecVerts.push_back(b2Vec2(-632.2f / 100.0, 5.3f / 100.0));
vecVerts.push_back(b2Vec2(-603.9f / 100.0, 17.3f / 100.0));
vecVerts.push_back(b2Vec2(-536.0f / 100.0, 18.0f / 100.0));
vecVerts.push_back(b2Vec2(-518.3f / 100.0, 28.6f / 100.0));
vecVerts.push_back(b2Vec2(-282.1f / 100.0, 13.1f / 100.0));
vecVerts.push_back(b2Vec2(-258.1f / 100.0, 27.2f / 100.0));
vecVerts.push_back(b2Vec2(-135.1f / 100.0, 18.7f / 100.0));
vecVerts.push_back(b2Vec2(9.2f / 100.0, -19.4f / 100.0));
vecVerts.push_back(b2Vec2(483.0f / 100.0, -18.7f / 100.0));
vecVerts.push_back(b2Vec2(578.4f / 100.0, 11.0f / 100.0));
vecVerts.push_back(b2Vec2(733.3f / 100.0, -7.4f / 100.0));
vecVerts.push_back(b2Vec2(827.3f / 100.0, -1.1f / 100.0));
vecVerts.push_back(b2Vec2(1006.9f / 100.0, -20.2f / 100.0));
vecVerts.push_back(b2Vec2(1023.2fdddddd / 100.0, -20.2f / 100.0));
i = vecVerts.size();


//I would like to pass this sets of calculations to the stitch method below rather
 than do it here

vector<b2Vec2>::iterator pos;

//add y offset value to our b2Vec2
for(pos = vecVerts.begin();pos != vecVerts.end();++pos)

{
    //get b2Vec2 value at index
    b2Vec2 currVert = *pos;

    //add y offset (this will come from the sprite image size latterly, set value for testing only
    b2Vec2 addVert = b2Vec2(currVert.x,currVert.y + 40 /PTM_RATIO); 

    //copy offset added b2Vec2 back to vector as index
    pos->b2Vec2::operator=(addVert);
}


 //currently using this as kludge to pass my vector to the stitch method
b2Vec2 * chain = &vecVerts[0];
[self stitchterrainvertswith:chain num:i];

这是我当前的方法,将我的向量作为C样式数组传递

-(void)stitchterrainvertswith:(b2Vec2 *)verts num:(int)num {


//create bodydef
b2BodyDef groundBodyDef;

//set body as static
groundBodyDef.type = b2_staticBody;

//set body position 
groundBodyDef.position.Set(0, 0);

//create body using def
groundBody = world->CreateBody(&groundBodyDef);

//create shapes

b2EdgeShape screenEdge;
b2ChainShape terrain;

terrain.CreateChain(verts, num);
  groundBody->CreateFixture(&terrain,0);

//keeps track of max x value for all the ground pieces that are added to the scene
   //maxVerts.x += totalXVerts.x;
    }

我尝试使用stj :: vector的objc包装器,但在这里有点丢失是我的例子:

VecWrap.h
#import "Box2D.h"
#include <vector>

struct VecAcc;

@interface VecWrap : NSObject
{
struct VecAcc* vec;
}
@end

VecWrap.MM

#import "VecWrap.h"

struct VecAcc {
std::vector<b2Vec2>data;
};


@implementation VecWrap


-(id)init 
{
    vec = 0;
    if (self == [super init]) {
    vec = new VecAcc;
}
   return self;
}

-(void)dealloc 

{
delete vec;
[super dealloc];
}
@end

然后创建以下方法:

-(void)stitchgroundvectswith:(VecAcc*)vecs num:(int)num;

哪个不起作用甚至可能？

Answer 1

一切都正确,Barry Wark的解决方案有效,但我不推荐它,因为像这样的语言特定的预处理器技巧是脆弱的IMO.特别是,如果涉及名称空间,它们将无法正常工作,并且只能处理指针.

首先,我强烈建议开发人员尽可能地将他们的ObjC和C++分开,并将ObjC++最小化到一些真正需要它的地方.ObjC++是一种疯狂的语言,gdb经常遇到麻烦,损害ARC性能,编译速度较慢,而且通常大多是有用的黑客而不是真正的语言.

我建议这种方法在头文件中隐藏来自ObjC的C++方法:

@interface MyClass

- (void)anOtherMethodCalledFromObjC;

#ifdef __cplusplus
- (void)stitchGroundVectsWithVector:(std::vector<b2Vec2>)vec;
#endif
@end

但一般来说,我建议大多数程序都是.m和.cpp文件,并带有几个.mm文件将它们粘合在一起.

有关如何在旧代码中执行此操作的详细讨论,请参阅包装C++ - Take 2.较新的代码不要求标题中包含ivars,因此今天应该更简单.