C

• rarely used for end-user apps
• more often used for
  • components e.g. CPython, Linux Kernel, EMACS...
  • tools meant for developers

Difference between C++ and C

main difference: C++ has classes and objects

// pointer to a function
int (*v)(float f, char c)
// ^ pointer v that points to a function that accept float f and char c and return int
return _Generic(E, 
				float: 1,
				long: 2,
				default: -1)
// if E's type is float, return 1, long :2 
#define absv(x) _Generic(x,
		float: x < 0 ? -x : x;
		double: x < 0 ? -x : x;
		default: (x == INT_MIN? abort() : x < 0 ? -(x) : x);

POSIX: assume we have access to OS

C: programming standard can run without OS, support atomic access

Architecture of C/C++ Environment

(below are layers, from high to low)

• .c, .cpp files → gcc⬇️
• .s files → as ⬇️
• some .o files, some libraries → ld ⬇️
• metadata instructions in a file (OS loader⬇️) an executable file (a.out)
• OS Kernel , syscalls | your program's machine instructions
• machine level: x86-64, ARM 64, RISC-V, ...

C Compilers

gcc, clang, icc, nvcc, and some others that are tuned for architectures

Compiler Portability