how to initialize const char** array

Question

This is my code

Here's the header file.

class ShaderManager {
private:

const GLchar** vertexShaderCode_color;
const GLchar** fragmentShaderCode_color;
const GLchar** vertexShaderCode_texture;
const GLchar** fragmentShaderCode_texture;
ShaderManager();
~ShaderManager();

cpp file. in constructor

vertexShaderCode_color = {
    "uniform mat4 uMVPMatrix;\n"
    "attribute vec4 vPosition;\n"
    "void main() { \n"
    "   gl_Position = uMVPMatrix * vPosition; \n"
    "}\n"
};
fragmentShaderCode_color = {
    "precision mediump float;\n"
    " uniform vec4 vColor;\n"
    "void main() {\n"
    "gl_FragColor = vColor;\n"
    "}\n"
};
vertexShaderCode_texture = {
    "uniform mat4 uMVPMatrix;\n"
    "attribute vec4 vPosition;\n"
    "attribute vec2 texCoord;\n"
    " varying vec2 texCoordOut;\n"
    "void main() {\n"
    "gl_Position = uMVPMatrix * vPosition;\n"
    "texCoordOut = texCoord;\n"
    "}\n"
};
fragmentShaderCode_texture = {
    "precision mediump float;\n"
    "varying vec2 texCoordOut;\n"
    "uniform sampler2D u_texture;\n"
    "uniform vec4 vColor;\n"
    " void main() {\n"
    "  vec4 texColor = texture2D(u_texture, texCoordOut);\n"
    "  gl_FragColor = texColor;\n"
    "}\n"
};

It's not working. The error message is:

Error 3 error : cannot convert '' to 'const GLchar** {aka const char**}' in assignment D:\\workspace\\VS2013\\Projects\\bbEngine2\\bbEngine2\\src\\GLManager\\ShaderManager.cpp 10 2 bbEngine2

Answer 1

how to initialize const char** array

In the same way as every other array.

const GLchar** vertexShaderCode_color;

That's not a const char** array. It's a single pointer to const GLchar* .

vertexShaderCode_color = {
    "uniform mat4 uMVPMatrix;\n"
    "attribute vec4 vPosition;\n"
    "void main() { \n"
    "   gl_Position = uMVPMatrix * vPosition; \n"
    "}\n"
};

That is indeed how to initialize an array. But as I already pointed out, you didn't declare vertexShaderCode_color as an array. It's a pointer. Also, if that's inside the constructor body, then the member is already initialized. You annot assign to an array.

If you indeed want vertexShaderCode_color to be an array, then you need to declare it as an array. Remember that sizes of arrays must be known at runtime:

const char* vertexShaderCode_color[5];

And then initialize it in the member initializer list or in a default member initializer.

Answer 2

I think you need something like:

static const char* vertexShaderCode_color_value[] = {
    "uniform mat4 uMVPMatrix;\n"
    "attribute vec4 vPosition;\n"
    "void main() { \n"
    "   gl_Position = uMVPMatrix * vPosition; \n"
    "}\n"
};
vertexShaderCode_colour = vertexShadeCode_colour_value;

You are being hit by the subtle difference between arrays and pointers in C and C++.

Edit: I thought you needed to namespace qualify the variable, but I see this is in the constructor ... in which case if you can't use a static variable for the value, you need to do some memory allocation:

In class definition:

std::vector<const GLChar*> vertexShaderCode_color_value;
GLChar** vertexShaderCode_color;  // Order is significant.

In initializer list:

    vertexShaderCode_colour_value { ... },
    vertexShaderCode_colour { &vertexShaderCode_colour_value.front() },

(or do it in the constructor body if you prefer)