How do you read directly from physical memory?

Question

In C or C++ (windows), how do you read RAM by giving a physical (not virtual) address? That means without going trough virtual memory system (mmu tables), and being specific

Answer 1

Neither the language C, nor C++ defines the term "memory". Things are defined in abstract terms like "storage" and "storage classifiers". Pointers are abstract things -- their values can be anything, totally unrelated to the physical or virtual addresses.

Only in the context of a system and its implementation are terms like memory and address space introduced. And since those are system specific things, one must use the methods provided by the OS to access them.

Even when implementing an OS kernel you have to do access to lowest level stuff not through C (because it simply can't), but through methods specific to implementation and architecture. Usually this is done through a set of low level functions programmed in assembly, which are written in a way that they match the kind of machine code the compiler generates. This allows those functions written in assembly to be called from C as if they were compiled by the compiler.