我不知道如何为 sizeof() 和 void 指针取消引用该指针

Question

我不知道如何取消引用这个指针...

sizeof(shapetest2->tripsName) 在下面这一行中，它显然不起作用，因为它是一个指针，我不知道如何取消引用它？ （这很容易吗？还是需要几个步骤？我已经尝试了几种方法，但无法接近）我没有足够的经验来解决这种特殊情况。

glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(shapetest2->tripsName), shapetest2->tripsName);

这是设置代码。 （我正在 openGL ES 1.5 中试验 VOB，所以如果它看起来很奇怪，这就是原因）如果我忘记了一些重要的设置或定义或代码，请告诉我，我将包括它。

GLsizeiptr dataSize;
GLsizeiptr indexSize;

typedef struct shapeBase {
    void *stripsName[maxStrips];
    void *tripsName;
    void *fansName;
    int   totStrips;
    int   stripsNum[maxStrips];
    int   tripsNum;
    int   totFans;
    int   fansBgn[maxStrips];
    int   fansNum[maxStrips];
    void *dataName;
    void *listOfInserts;
    Vertex3D center;
    Vertex3D radius;
    int   damageMax;
    float weight;
    GLuint bufferName;
    GLuint indexName;
} shapeBase;

static const GLushort test2Trips[] =
{
    0, 1, 3, 1, 2, 3,
    4, 5, 7, 5, 6, 7,
    8, 9, 11, 9, 10, 11,
    12, 13, 15, 13, 14, 15,
    16, 17, 19, 17, 18, 19,
    20, 21, 23, 21, 22, 23,
    24, 25, 27, 25, 26, 27,
    28, 29, 31, 29, 30, 31,
    32, 33, 35, 33, 34, 35,
    36, 37, 39, 37, 38, 39,
    40, 41, 43, 41, 42, 43,
    44, 45, 47, 45, 46, 47,
};

//-------------------------
static inline void shapetest2Setup(void)
{
    shapetest2 = malloc(sizeof(shapeBase));
    shapetest2->stripsName[1]   = NULL;
    shapetest2->tripsName       = &test2Trips;
    shapetest2->fansName        = NULL;
    shapetest2->dataName        = &test2Data;
    shapetest2->totStrips       = 0;
    shapetest2->stripsNum[1]    = 0;
    shapetest2->tripsNum        = 72;
    shapetest2->totFans     = 0;
    shapetest2->listOfInserts   = NULL;
    shapetest2->center      = Vertex3DMake( 0.000000, -0.000000, 2.000000 );
    shapetest2->radius      = Vertex3DMake( 1.000000, 1.000000, 2.000000 );

    dataSize = sizeof(test1Data) + sizeof(test2Data);

    glGenBuffers(1, &mainBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);
    glBufferData(GL_ARRAY_BUFFER, dataSize, NULL, GL_STATIC_DRAW);

    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(test1Data), test1Data);
    glBufferSubData(GL_ARRAY_BUFFER, sizeof(test1Data), sizeof(test2Data), test2Data);

//  glGenBuffers(1, &shapetest2->indexName);
//  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, shapetest2->indexName);
//  glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(test2Trips), test2Trips, GL_STATIC_DRAW);


    indexSize = sizeof(test1Trips) + sizeof(test2Trips);

    glGenBuffers(1, &mainIndex);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mainIndex);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indexSize, NULL, GL_STATIC_DRAW);
}


//------------------------------------------------------
static inline void DrawOutShape(void)
{
    glBindBuffer(GL_ARRAY_BUFFER, mainBuffer);


    glVertexPointer(3, GL_FLOAT, sizeof(VertexData3D), (void*)0);
    glNormalPointer(GL_FLOAT, sizeof(VertexData3D), (void*)12);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mainIndex);

//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(theInsert->insertName->tripsName), theInsert->insertName->tripsName);

//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(test1Trips), test1Trips);
//  glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, sizeof(test1Trips), sizeof(test2Trips), shapetest2->tripsName);

    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(shapetest2->tripsName), shapetest2->tripsName);


         glDrawElements(GL_TRIANGLES, theInsert->insertName->tripsNum, GL_UNSIGNED_SHORT, (void*)0);


    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);


polys += theInsert->insertName->tripsNum;

}

（theInsert 是 shapetest2 的句柄（指向指针的指针），因此如果您看到“theInsert->insertName”，则可以替换 shapetest2）

如果我注释掉有问题的行，并取消注释上面的行，它正在工作，但我需要这种间接，（实际上我需要另一个级别的间接，你可以在另一个注释掉的行中看到）但是如果我能弄清楚如何取消引用该行，我应该能够为另一个级别做到这一点间接？）

Answer 1

sizeof 是编译时常量，适用于您提供的确切类型。 void* 的 sizeof 只是您机器上指针的大小（可能是 4/8 字节）。只需将大小与其他数据一起存储即可。