openGLES vertex pointer problem

I'm new to openGLES (and to openGL too) and i have a problem...

I have a struct strip:

struct Vertex2F
{
    GLfloat x;
    GLfloat y;
};

struct Vertex3F
{
    GLfloat x;
    GLfloat y;
    GLfloat z;
};

struct Color4UB
{
    GLubyte r;
    GLubyte g;
    GLubyte b;
    GLubyte a;
};

struct Vertex
{
    Vertex3F pos;
    Color4UB color;
    Vertex2F tex;
};

struct Strip
{
    Strip() {vertices = 0; count = 0;}
    Strip(int cnt);
    ~Strip();
    void allocate(int cnt);
    void draw();
    Vertex *vertices;
    int count;
};

And i want do render GL_TRIANGLE_STRIP. Here is the code:

const int size = sizeof(Vertex);
long stripOffset = (long) &strip_;

int diff = offsetof(Vertex, pos); //diff = 0
glVertexPointer(3, GL_FLOAT, size, (void*)(stripOffset + diff));

It shows something strange after rendering with glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); if shows at all. But this code works as expected:

GLfloat ar[4*3];
for 开发者_开发百科(int i = 0; i < 4; ++i)
{
    ar[3*i + 0] = strip_.vertices[i].pos.x;
    ar[3*i + 1] = strip_.vertices[i].pos.y;
    ar[3*i + 2] = strip_.vertices[i].pos.z;
}
glVertexPointer(3, GL_FLOAT, 0, (void*)(ar));

Please explain me what am i doing wrong in first case ?

_strip.vertices is a pointer. I assume it is allocated dynamically. So the data in _strip.vertices is not just stored at the beginning of _strip, but at some different place and _strip.vertices just points there. So just use

long stripOffset = (long) strip_.vertices;

instead of

long stripOffset = (long) &strip_;