Const pointer to pointer to char problems

Const pointer to pointer to char problems

Ariesnl

Member #2,902

November 2002

I would like to manage OpenGL shaders in a more C++ and OO way
So I wanted to write a class for it..
However I run into trouble making the shader code a bit more managable..

I want to store the shader code into my class and then compile it

OpenGL expects a constant pointer to a pointer to a char "const **GLchar"
Right now I have an array of Glchar where the shadercode is stored..

Is there any good way to stuff one into the other ??

Maybe it's me but I don't see it....

#SelectExpand
  1bool OpenGLShader::Compile()
  2{
  GLchar source[m_vShaderSource.size()+2];
  vector<GLchar>::const_iterator P = m_vShaderSource.begin();
  int nIndex =0;
  while (P!=m_vShaderSource.end())
  {
      source[nIndex] = *P;
      nIndex++;
      P++;
  }
 12
  source[nIndex] ='\0';                               // <-------

  const GLchar ** pSource = &source;                  // <--------
  glShaderSource(m_nShaderIndex, 1, pSource, NULL);   // <---------
 17
 18
  glCompileShader(m_nShaderIndex);
  GLint status;
  glGetShaderiv(m_nShaderIndex, GL_COMPILE_STATUS, &status);
  if (status!=GL_TRUE)
  {
     glGetShaderInfoLog(m_nShaderIndex, 512, NULL, m_StatusBuffer);
     return false;
  }
  else
  {
      return true;
  }
 31}

Thanks...

Perhaps one day we will find that the human factor is more complicated than space and time (Jean luc Picard)
Current project: [Star Trek Project ] Join if you want ;-)

Edgar Reynaldo

Major Reynaldo

May 2007

Does casting work? A const** to GLchar just means you cant change the GLchars in the array.

const ** GLChar psource = (const ** GLCchar)&source;

One thing to ask is do you need to make it a 2d array? Right now you just have an array, or a 2d array with one row. What does the shader expect?

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Ariesnl

Member #2,902

November 2002

#SelectExpand
  1const GLchar* vertexSource =
  "#version 150 core\n "
  "in vec2 position;   "
  "in vec3 ColorIn;    "
  "out vec3 ColorFragment;  "
  "void main()"
  "{"
  "ColorFragment = ColorIn;"
  "gl_Position = vec4(position, 0.0, 1.0);"
  "}";

This code compiles on the graphics card so I think I need a 2D array...

Perhaps one day we will find that the human factor is more complicated than space and time (Jean luc Picard)
Current project: [Star Trek Project ] Join if you want ;-)

Edgar Reynaldo

Major Reynaldo

May 2007

It doesn't just expect a concatenated string? A single one?

Arthur Kalliokoski

Second in Command

February 2005

It compiles to one long string.

00001c60  69 6e 67 00 25 73 00 00  23 76 65 72 73 69 6f 6e  |ing.%s..#version|
00001c70  20 31 35 30 20 63 6f 72  65 0a 20 69 6e 20 76 65  | 150 core. in ve|
00001c80  63 32 20 70 6f 73 69 74  69 6f 6e 3b 20 69 6e 20  |c2 position; in |
00001c90  76 65 63 33 20 43 6f 6c  6f 72 49 6e 3b 20 6f 75  |vec3 ColorIn; ou|
00001ca0  74 20 76 65 63 33 20 43  6f 6c 6f 72 46 72 61 67  |t vec3 ColorFrag|
00001cb0  6d 65 6e 74 3b 20 76 6f  69 64 20 6d 61 69 6e 28  |ment; void main(|
00001cc0  29 7b 43 6f 6c 6f 72 46  72 61 67 6d 65 6e 74 20  |){ColorFragment |
00001cd0  3d 20 43 6f 6c 6f 72 49  6e 3b 67 6c 5f 50 6f 73  |= ColorIn;gl_Pos|
00001ce0  69 74 69 6f 6e 20 3d 20  76 65 63 34 28 70 6f 73  |ition = vec4(pos|
00001cf0  69 74 69 6f 6e 2c 20 30  2e 30 2c 20 31 2e 30 29  |ition, 0.0, 1.0)|
00001d00  3b 7d 00 00 00 00 00 00  00 00 50 c1 00 00 c0 3f  |;}........P....?|

They all watch too much MSNBC... they get ideas.

Thomas Fjellstrom

Member #476

June 2000

Multiple literal strings that are one after the other get concatenated.

--
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Edgar Reynaldo

Major Reynaldo

May 2007

yeah, that's kind of what I meant

Arvidsson

Member #4,603

May 2004

If you want to use a std::string: http://stackoverflow.com/questions/6047527/how-to-convert-stdstring-to-const-char

bamccaig

Member #7,536

July 2006

So basically it wants a pointer to a string? &source should be your "C string" (that is, a pointer to the beginning of the array of characters) so you may need to store that somewhere in order to take the address of that?

const GLchar * str = &source;
const GLchar ** ptr = &str;
//    Here, eat ^ that and leave us alone!

Append:

That said, a non-const pointer to a string suggests that they may wish to change it on you, which may or may not throw you for a loop... Do make sure that what you're trying is safe.

--
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