SDS understanding in redis

1.C In language char* What's the problem ？

1. Will '/0' As the terminator of a string , So you can't store '/0' character .
2. len(String) Operation requires O（n） Time complexity of .
3. strcat(des,src) When you add it , Will traverse to des The end is being appended , High time complexity .
4. char* Memory alignment is used by default , Wasted memory space .

2.Redis Customize SDS Reading ？

1. SDS：Simple Dynamic String, Simple dynamic String, Be similar to Go Medium slice. The data structure is shown below ：

 2.SDS Store the length of the actual string and the actual memory size , It can be more convenient len（） And string 、

 3.struct __attribute__ ((__packed__)) Storage in a compact way can save memory space ,flags Used to mark the length used for storage . Here is flags=sdshdr8 Data structure of .

struct __attribute__ ((__packed__)) sdshdr8 { uint8_t len; /*  The existing length of the character array */ uint8_t alloc; /*  Allocated space for character array , Excluding structures and \0 End character */ unsigned char flags; /* SDS type */ char buf[]; /* A character array */ };