c_notebook

Introduction

• This is a Linux c programming learning notebook
• Ref:
  Linux C编程一站式学习
  C语言程序设计 The C Programming Language

Supported

• os
  • Ubuntu 16.04 LTS
• compiler
  • gcc version 9.4.0

char

• char is a short integer, only 1B(8 bit)

• type conversion(or typecasting)

  int a = '1' - '0'	/* char int to digit */
  printf("%d\n", a);

• char array, refers array storing chars

  char ca[];

pointer*

• void * can be casted to any pointer without losing information

• pointer is a variable, hexademical int, different to array name

  int ia[4] = {0, 1, 2, 3};
  int *pa = ia;
  pa++	/* right */
  ia++	/* wrong, only variable can*/

Struct

• Store many different type variables

  struct Pointer {
      int x = 0;
      int y = 0;
  };	/* struct Pointer */
  struct Pointer p;	/* instantiation */

function()

• function returning a pointer

  Void *fun(int);

• pointer to a function

  void (*pfun) (int);

• function parameter

  void fun(char s[]);
  void fun(char *s);	/* char s[] same as char *s and char *s mostly used */

array[]

• pointer array, refers to array storing pointers

  int *ia[100];
  char *ca[100] = {"string", "hello", "world"};	/* mostly used to save string */
  printf("%s %s %s\n", ca[0], ca[1], ca[2], ca[3]);

• pointer to an array

  int (*pa)[100];

• array name, refers to a pointer to the first element of array

  int ia[10]; 
  printf("%p %p", ia, &ia[0])  /* ia same as &ia[0]; */

• index, refers to dereference address

  /* ia[i] same as *(ia + i) */