OpenGL: Zero active uniforms - c++

Question

I'm referring to the OpenGL SuperBible. I use their framework to create an own program. I wanted to do something with an Interface Block (specifically a Uniform Block). If I call
glGetActiveUniformsiv(program, 1, uniformIndices, GL_UNIFORM_OFFSET, uniformOffsets);
I get an error, namely GL_INVALID_VALUE.
But if I call the same function with a 0 instead of a 1, it doesn't make that error. I assumed then, that I have no active uniforms. I should have 3 of them, however.
How do I activate them? Here's my shader:
#version 450 core
layout (location = 0) in vec4 position;
layout (location = 1) in vec4 color;
out vec4 vs_color;
uniform TransformBlock {
mat4 translation;
mat4 rotation;
mat4 projection_matrix;
};
void main(void)
{
mat4 mvp = projection_matrix * translation * rotation ;
gl_Position = mvp * position;
vs_color = color;
}
Here is some code from the startup method:
static const GLchar* uniformNames[3] = {
"TransformBlock.translation",
"TransformBlock.rotation",
"TransformBlock.projection_matrix",
};
GLuint uniformIndices[3];
glUseProgram(program);
glGetUniformIndices(program, 3, uniformNames, uniformIndices);
GLint uniformOffsets[3];
GLint matrixStrides[3];
glGetActiveUniformsiv(program, 3, uniformIndices, GL_UNIFORM_OFFSET, uniformOffsets);
glGetActiveUniformsiv(program, 3, uniformIndices, GL_UNIFORM_MATRIX_STRIDE, matrixStrides);
unsigned char* buffer1 = (unsigned char*)malloc(4096);
//fill buffer1 in a for-loop
GLuint block_index = glGetUniformBlockIndex(program, "TransformBlock");
glUniformBlockBinding(program, block_index, 0);
glBindBufferBase(GL_UNIFORM_BUFFER, 0, (GLuint)buffer1);
free(buffer1);
However, as a consequence of the function returning GL_INVALID_VALUE there's an error with the calls:
*((float *)(buffer1 + offset)) = ...
and the whole program interrupts. Without adding the offset, I don't get an error here, so I think the second error depends on the first error.

Answer 1

I think it goes wrong at glGetUniformIndices, because you prefixed your uniform names with TransformBlock. You don't use that to access the uniforms with that prefix in the GLSL code, either. If you wanted that, you'd had to set an instance name for the uniform block, the block name is not relevant for accessing / naming the uniforms at all. It is only used for matching interfaces if you link together multiple shaders accessing the same interface block.