covering each side of a cube with different images- OpenGL - c++

Question

I have this cube and I want to cover each side of it with a different image in which a letter appears.
My problem is that cube is covered by the same image, as you can see in following image.
but I want that letter A appears on top, B on left side and C on right side.
in order to convert/transform images (letters A,B,C) in textures I use this code:
glGenTextures(1, textureA);
glGenTextures(1, textureB);
glGenTextures(1, textureC);
glClearColor (0.0, 0.0, 0.0, 0.0);
if (flagA ==1){
cvtColor(imageA, imageA, CV_BGR2RGB);
glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, textureA);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
//glTexImage2D(GL_TEXTURE_2D, 0, 4,image.cols, image.rows, 0, GL_RGB,GL_UNSIGNED_BYTE, image.data);
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, imageA.cols, imageA.rows, GL_RGB, GL_UNSIGNED_BYTE, imageA.data);
}
if (flagC ==1){
cvtColor(imageC, imageC, CV_BGR2RGB);
glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, textureC);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
//glTexImage2D(GL_TEXTURE_2D, 0, 4,image.cols, image.rows, 0, GL_RGB,GL_UNSIGNED_BYTE, image.data);
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, imageC.cols, imageC.rows, GL_RGB, GL_UNSIGNED_BYTE, imageC.data);
}
if (flagB ==1){
cvtColor(imageB, imageB, CV_BGR2RGB);
glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, textureB);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
//glTexImage2D(GL_TEXTURE_2D, 0, 4,image.cols, image.rows, 0, GL_RGB,GL_UNSIGNED_BYTE, image.data);
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, imageB.cols, imageB.rows, GL_RGB, GL_UNSIGNED_BYTE, imageB.data);
}
I noted that if I switch block if(flagB==1){...} with if(flagC==1){...} (in this way image with C letter is the last in process of image-texture transformation), my cube is covered only by C letters.
Why this strange behaviour?
In order to display the result, I use this code:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, WIDTH, HEIGHT, 0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
if(flagA==1){
glBindTexture(GL_TEXTURE_2D, textureA);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex2f((GLfloat)((A[3].x)),(GLfloat)(A[3].y));
glTexCoord2f(1.0f, 0.0f); glVertex2f((GLfloat)((A[0].x)),(GLfloat)(A[0].y));
glTexCoord2f(1.0f, 1.0f); glVertex2f((GLfloat)((A[1].x)),(GLfloat)(A[1].y));
glTexCoord2f(0.0f, 1.0f); glVertex2f((GLfloat)((A[2].x)),(GLfloat)(A[2].y));
glEnd();
}
if(flagB==1){
glBindTexture(GL_TEXTURE_2D, textureB);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex2f((GLfloat)((B[3].x)),(GLfloat)(B[3].y));
glTexCoord2f(1.0f, 0.0f); glVertex2f((GLfloat)((B[0].x)),(GLfloat)(B[0].y));
glTexCoord2f(1.0f, 1.0f); glVertex2f((GLfloat)((B[1].x)),(GLfloat)(B[1].y));
glTexCoord2f(0.0f, 1.0f); glVertex2f((GLfloat)((B[2].x)),(GLfloat)(B[2].y));
glEnd();
}
if(flagC==1){
glBindTexture(GL_TEXTURE_2D, textureC);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex2f((GLfloat)((C[3].x)),(GLfloat)(C[3].y));
glTexCoord2f(1.0f, 0.0f); glVertex2f((GLfloat)((C[0].x)),(GLfloat)(C[0].y));
glTexCoord2f(1.0f, 1.0f); glVertex2f((GLfloat)((C[1].x)),(GLfloat)(C[1].y));
glTexCoord2f(0.0f, 1.0f); glVertex2f((GLfloat)((C[2].x)),(GLfloat)(C[2].y));
glEnd();
}
I work on windows7 x64 and OpenGL.

Answer 1

We don't see your rendering code.
Did you write this somewhere to generate the texture ids ?
glGenTextures(1, &textureA);
glGenTextures(1, &textureB);
glGenTextures(1, &textureC);
Did you write this when you are rendering your cube ?
glBindTexture(GL_TEXTURE_2D, textureA);
// Draw the A face
glBindTexture(GL_TEXTURE_2D, textureB);
// Draw the B face
glBindTexture(GL_TEXTURE_2D, textureC);
// Draw the C face

Answer 2

What you are doing is:
glGenTextures(1, textureA);
glGenTextures(1, textureB);
glGenTextures(1, textureC);
It should be:
glGenTextures(1, &textureA);
glGenTextures(1, &textureB);
glGenTextures(1, &textureC);
I assume the problem happens because the variables textureA, textureB and textureC do not get valid values and therefore glBindTexture calls are doing nothing (although i think you should have got segmentation fault).