C/C++ function definitions without assembly

Question

I always thought that functions like printf() are, in the last step, defined using inline assembly. That deep in the bowels of stdio.h is buried some asm code t

Answer 1

The standard library functions are implemented on an underlying platform library (e.g. UNIX API) and/or by direct system calls (that are still C functions). The system calls are (on platforms that I know of) internally implemented by a call to a function with inline asm that puts a system call number and parameters in CPU registers and triggers an interrupt that the kernel then processes.

There are also other ways of communicating with hardware besides syscalls, but these are usually unavailable or rather limited when running under a modern operating system, or at least enabling them requires some syscalls. A device may be memory mapped, so that writes to certain memory addresses (via regular pointers) control the device. I/O ports are also often used and depending the architecture these are accessed by special CPU opcodes or they, too, may be memory mapped to specific addresses.