cstack/db_tutorial

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P01

• REPL (read-execute-print loop)
  • 读取﹣求值﹣输出循环 / 交互式顶层构件
  • 一个编程环境. 因它能立刻对初学者做出回应. 对学习一门语言具有很大的帮助.
  • via: Read–eval–print loop - Wikipedia
• ✖ B Tree
  • via: Youtube-29:45.
• size_t & ssize_t
  • size_t
    • 32 Bit: typedef unsigned int size_t;.
    • 64 Bit: typedef unsigned long size_t;.
    • 注意写函数的时候, 无符号数不要和符号数比较.

        #include <stdio.h>
        #include <string.h>
        int main(){
            int i = -1;
            if(i > strlen("Demon")) printf("Hello World");
            else printf("Hello Demon");
            return 0;
        } //Hello World via http://demon.tw/programming/c-size_t-pitfall.html

- `ssize_t `
  - 32 Bit: `int`.
  - 64 Bit: `long int`.
  - via: https://blog.csdn.net/bzhxuexi/article/details/19899803 & https://stackoverflow.com/questions/2550774/what-is-size-t-in-c

• getline in C.

      // from https://c-for-dummies.com/blog/?p=1112
      #include <stdio.h>
      int input(char *s,int length);
      int main(){
          char *buffer;
          size_t bufsize = 32;
          size_t characters;
          buffer = (char *)malloc(bufsize * sizeof(char));
          if( buffer == NULL){
              perror("Unable to allocate buffer");
              exit(1);
          }
          printf("Type something: ");
          characters = getline(&buffer,&bufsize,stdin);
          printf("%zu characters were read.\n",characters);
          printf("You typed: '%s'\n",buffer);
          return(0);
      }
      // case two
      #include <stdio.h>
      int input(char *s,int length);
      int main()
      {
          char *b;
          size_t bufsize = 0;
          size_t characters;
          printf("Type something: ");
          characters = getline(&b, &bufsize, stdin);
          printf("%ld\n", bufsize);
          printf("%zu characters were read.\n", characters);
          printf("You typed: '%s'\n", b);
          return(0);
      }

  - 会发现在 `char` 指针做缓冲区的时候, `bufsize` 默认为 `120`, 就算读入缓冲超过 `120` , 也会加倍为`240`. 但是, char 指针可以

        > ./test
        Type something: dsdsa
        120
        6 characters were read.
        You typed: '����'
        > ./test
        Type something: testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttestt
        240
        130 characters were read.
        You typed: 'testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttestt
        '

  - more via: https://stackoverflow.com/questions/20036074/length-of-line-in-getline-function-c.

P02

• .exit: “meta-commands”
• strncmp: the “insert” keyword will be followed by data.

P03

• name: HTH full: Hope That Helps description: used in electronic messages when you have told someone something or done something for them via: https://www.macmillandictionary.com/dictionary/british/hth type: abbr
• uint8_t / uint16_t / uint32_t / uint64_t in system-c id: 629d9e2c-2c0c-48db-ae2d-56eba8649d36
  • 这些类型的来源：这些数据类型中都带有 _t, _t 表示这些数据类型是通过 typedef 定义的，而不是新的数据类型。也就是说，它们其实是我们已知的类型的别名。
  • 使用这些类型的原因：方便代码的维护。比如，在 C 中没有 bool 型，于是在一个软件中，一个程序员使用 int，一个程序员使用 short，会比较混乱。最好用一个 typedef 来定义一个统一的 bool：
  • 在涉及到跨平台时，不同的平台会有不同的字长，所以利用预编译和 typedef 可以方便的维护代码。 via: 浅析C语言之uint8_t / uint16_t / uint32_t /uint64_t
  • 在 C99 标准中定义了这些数据类型，具体定义在：/usr/include/stdint.h ISO C99: 7.18 Integer types

        #ifndef __int8_t_mark: d
        # mark:  __int8_t_mark: d
        typedef signed char             int8_t;
        typedef short int               int16_t;
        typedef int                     int32_t;
            # if __WORDSIZE == 64
                typedef long int                int64_t;
            # else
            __extension__
            typedef long long int           int64_t;
            # endif
        #endif
        typedef unsigned char           uint8_t;
        typedef unsigned short int      uint16_t;
        #ifndef __uint32_t_mark: d
            typedef unsigned int            uint32_t;
            # mark:  __uint32_t_mark: d
        #endif
        #if __WORDSIZE == 64
            typedef unsigned long int       uint64_t;
        #else
            __extension__
            typedef unsigned long long int  uint64_t;
        #endif

  -        > [When should one use the datatypes from stdint.h?](https://stackoverflow.com/questions/20077313)
    - When the programming tasks specify the integer width especially to accommodate some file or communication protocol format.
    - When high degree of *portability* between platforms is required over *performance*.
  - `uint32_t` means `unsigned int 32 type`. via: https://stackoverflow.com/questions/48833976 & https://stackoverflow.com/questions/231760

• Strcut, Typedef

      // via: https://stackoverflow.com/questions/17720223
      truct {
         ...
      } myNameStruct;  // mark: s myNameStruct as a variable with this struct
                       // definition, but the struct definition cannot be re-used.
      struct Name {
         ...
      } myNameStruct;  // mark:  a struct, and declare/mark:  a struct variable
               // at the same time:
      typedef struct {
         ...
      } Name_t;    // use an untagged struct type inside a typedef:
      typedef struct Name {
         ...
      } Name_t;    // begin with typedef, NewTypeName will be Name_t,
               // not a varible

• 序列化 (serialize): 把对象转化为可传输的字节序列过程称为序列化
• 反序列化 (deserialize): 把字节序列还原为对象的过程称为反序列化

P04

id: 629dbc40-678d-4e9e-bb94-3d03c9040a26