Pass two attributes into vertex shader(Qt5.0.2)

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platform : mac osx 10.8.3
compiler : clang3.2

Learning opengl from this website(ch2, playing with colors)
"opengl":http://www.arcsynthesis.org/gltut/

Trying to pass my data into two attributes, but the second attributes can't have the data correctly

vertex shader

attribute vec4 position;
attribute vec4 color;
 
varying vec4 theColor;
 
void main() {       
    gl_Position = position;
    theColor = color;
    //theColor = vec4(0.5, 0.8, 0.3, 1.0);
}

attribute vec4 position;
attribute vec4 color;

varying vec4 theColor;

void main() {       
    gl_Position = position;
    theColor = color;
    //theColor = vec4(0.5, 0.8, 0.3, 1.0);
}

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fragment shader

varying vec4 theColor;
 
void main()
{
    gl_FragColor = theColor;
}

varying vec4 theColor;

void main()
{
    gl_FragColor = theColor;
}

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initialize buffer

std::vector<GLfloat> const vertexPositions{
        0.75f,  0.75f, 0.0f, 1.0f,
        0.75f, -0.75f, 0.0f, 1.0f,
       -0.75f, -0.75f, 0.0f, 1.0f,
        1.0f, 0.0f, 0.0f, 1.0f,
        0.0f, 1.0f, 0.0f, 1.0f,
        0.0f, 0.0f, 1.0f, 1.0f
    };
 
    positionBufferObject.push_back(0);
 
    glGenBuffers(1, &positionBufferObject.back());
    glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject.back());
 
    glBufferData(GL_ARRAY_BUFFER, buffer.size() * sizeof(GLfloat), &buffer[0], GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

std::vector<GLfloat> const vertexPositions{
        0.75f,  0.75f, 0.0f, 1.0f,
        0.75f, -0.75f, 0.0f, 1.0f,
       -0.75f, -0.75f, 0.0f, 1.0f,
        1.0f, 0.0f, 0.0f, 1.0f,
        0.0f, 1.0f, 0.0f, 1.0f,
        0.0f, 0.0f, 1.0f, 1.0f
    };

    positionBufferObject.push_back(0);

    glGenBuffers(1, &positionBufferObject.back());
    glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject.back());

    glBufferData(GL_ARRAY_BUFFER, buffer.size() * sizeof(GLfloat), &buffer[0], GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

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paintGL

void ch2FragPosition::paintGL()
{       
    glClear(GL_COLOR_BUFFER_BIT);
    glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject[0]);
 
    int vertexLocation = program.attributeLocation("position");
    program.enableAttributeArray(vertexLocation);
    glVertexAttribPointer(vertexLocation, 4, GL_FLOAT, GL_FALSE, 0, 0);
 
    int colorLocation = program.attributeLocation("color");
    program.enableAttributeArray(colorLocation);
    glVertexAttribPointer(colorLocation, 4, GL_FLOAT, GL_FALSE, 0, (GLvoid const*)(12 * sizeof(GLfloat)));
 
    glDrawArrays(GL_TRIANGLES, 0, 3);
 
    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

void ch2FragPosition::paintGL()
{       
    glClear(GL_COLOR_BUFFER_BIT);
    glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject[0]);
    
    int vertexLocation = program.attributeLocation("position");
    program.enableAttributeArray(vertexLocation);
    glVertexAttribPointer(vertexLocation, 4, GL_FLOAT, GL_FALSE, 0, 0);

    int colorLocation = program.attributeLocation("color");
    program.enableAttributeArray(colorLocation);
    glVertexAttribPointer(colorLocation, 4, GL_FLOAT, GL_FALSE, 0, (GLvoid const*)(12 * sizeof(GLfloat)));

    glDrawArrays(GL_TRIANGLES, 0, 3);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

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The QGLWidget show me a black window, if I alter the vertex shader like these
QGLWidget will show me a triangle with color

attribute vec4 position;
attribute vec4 color;
 
varying vec4 theColor;
 
void main() {       
    gl_Position = position;
    //theColor = color;
    theColor = vec4(0.5, 0.8, 0.3, 1.0);
}

attribute vec4 position;
attribute vec4 color;

varying vec4 theColor;

void main() {       
    gl_Position = position;
    //theColor = color;
    theColor = vec4(0.5, 0.8, 0.3, 1.0);
}

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How could I fix this problem?Thanks

---

Added after 1 7 minutes:

I found the problem already, it has nothing to do with the opengl, I forgot to point the
class by a proper base class.

base class is : ch1HelloTriangle
derived class : ch2FragPosition

I declared the class liked this

std::unique_ptr<ch2FragPosition> ch2_frag_position(new ch2FragPosition(":ch2/modernOpenGLShader/ch2/positionVertex",
                                                                                  ":ch2/modernOpenGLShader/ch2/positionFrag"));
            ch2_frag_position->show();

std::unique_ptr<ch2FragPosition> ch2_frag_position(new ch2FragPosition(":ch2/modernOpenGLShader/ch2/positionVertex",
                                                                                  ":ch2/modernOpenGLShader/ch2/positionFrag"));
            ch2_frag_position->show();

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But it should be

std::unique_ptr<ch1HelloTriangle> ch2_frag_position(new ch2FragPosition(":ch2/modernOpenGLShader/ch2/positionVertex",
                                                                                  ":ch2/modernOpenGLShader/ch2/positionFrag"));
            ch2_frag_position->show();

std::unique_ptr<ch1HelloTriangle> ch2_frag_position(new ch2FragPosition(":ch2/modernOpenGLShader/ch2/positionVertex",
                                                                                  ":ch2/modernOpenGLShader/ch2/positionFrag"));
            ch2_frag_position->show();

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Thanks for your helps