Retrieving float values from framebuffer depth map - c++

Question

I have rendered a depth map to a framebuffer in the following way:
// the framebuffer
glGenFramebuffers(1, &depthMapFBO);
// completion: attacching a texture
glGenTextures(1, &depthMap);
glBindTexture(GL_TEXTURE_2D, depthMap);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32F, SCR_WIDTH, SCR_HEIGHT, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL); // i.e. allocate memory, to be filled later at rendering
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
// bind framebuffer and attach depth texture
glBindFramebuffer(GL_FRAMEBUFFER, depthMapFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthMap, 0);
glDrawBuffer(GL_NONE); // i.e. explicitly tell we want no color data
glReadBuffer(GL_NONE); // i.e. explicitly tell we want no color data
glBindFramebuffer(GL_FRAMEBUFFER, 0);
Note the use of GL_DEPTH_COMPONENT32F because I want a high precision.
Now I want to put the values stored in the depth buffer of the framebuffer into an array, preserving the precision. How to do so? Here is what I had in mind:
glBindFramebuffer(GL_FRAMEBUFFER, depthMapFBO);
glClear(GL_DEPTH_BUFFER_BIT);
[ render the scene to framebuffer]
GLfloat * d= new GLfloat[conf::SCR_WIDTH * conf::SCR_HEIGHT];
glReadPixels(0, 0, conf::SCR_WIDTH, conf::SCR_HEIGHT, GL_DEPTH_COMPONENT, GL_FLOAT, d);
for (int i{ 0 }; i < conf::SCR_HEIGHT; ++i) {
for (int j{ 0 }; j < SCR_WIDTH; ++j) {
std::cout << d[i * SCR_WIDTH + j] << " ";
}
std::cout << std::endl;
}
However, this always prints 0.956376. Why so? I know I still have to re-linearize the depths... but why is always printed a constant value, and how can I fix this? Furthermore, is my approach correct, with regards to the lossless retrieval of information? Thanks in advance.
The same thing happens with:
GLfloat * d= new GLfloat[conf::SCR_WIDTH * conf::SCR_HEIGHT * 4];
glBindTexture(GL_TEXTURE_2D, depthMap);
glGetTexImage(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, GL_FLOAT, d);