Redis source reading-sds string source reading

Redis uses SDS instead of char * strings,

It is defined as follows:

Char *SDS; struct SDSHDR {    int  len;     int  Free ;     Char buf[];};

SDS points to a char string

SDSHDR is the string header

More ingenious structure

Use char buf[] to store the actual contents of a string

Note Char *buf and Char buf[] are different

sizeof (SDSHDR) equals 8, not what I thought 12

The contiguous memory structure is as follows:

0----7 SDSHDR

8----After SDS, at the same time also buf position

Methods of establishing SDS

SDS Sdsnewlen (Const void*init, size_t Initlen) {    structSDSHDR *sh; if(init) {sh= Zmalloc (sizeof(structSDSHDR) +initlen+1); } Else{sh= Zcalloc (sizeof(structSDSHDR) +initlen+1); }    if(sh = = NULL)returnNULL; SH->len =Initlen; SH- Free=0; if(Initlen &&init) memcpy (Sh-buf, Init, Initlen); SH->buf[initlen] =' /'; return(Char*) sh->buf;}

Methods of releasing SDS

void Sdsfree (SDS s) {    ifreturn;    Zfree (S-sizeof(struct  sdshdr));}

Note that the SDS points to the actual string, not the SDSHDR.

There are many functions for processing SDS strings in SDS.C (after all, in order to replace char *)

 

Function name	Role	Complexity of
Sdsnewlen	Creates an SDS of a specified length, accepting a specified C string as the initialization value	O (N)
Sdsempty	Create an SDS that contains only the empty string ""	O (N)
Sdsnew	Creates a corresponding SDS based on the given C string.	O (N)
Sdsdup	Copy a given SDS	O (N)
Sdsfree	Releasing a given SDS	O (1)
Sdsupdatelen	Update the free and Len values for the SDSHDR corresponding to the given SDS	O (1)
Sdsclear	Clears the buf of the given SDS, initializes the BUF to "", and modifies the free and Len values of the corresponding SDSHDR	O (1)
Sdsmakeroomfor	Expansion of BUF for a given SDS corresponding to SDSHDR	O (N)
Sdsremovefreespace	Release the excess space of the BUF without altering the SDS	O (N)
Sdsallocsize	Calculates the memory size of a given SDS	O (1)
Sdsincrlen	Extend or shrink the right side of the BUF for a given SDS	O (1)
Sdsgrowzero	Expands the given SDS to the specified length, and the spare part is populated with the	O (N)
Sdscatlen	Appends a C string to the buf of the given SDS counterpart SDSHDR	O (N)
Sdscpylen	To copy a C string into SDS, it is necessary to determine whether an extension is required based on the total length of the SDS	O (N)
sdscatprintf	Append to the given SDS by formatting the output form	O (N)
Sdstrim	For a given SDS, delete the front/back end characters in the given C string	O (N)
Sdsrange	Intercept a given sds,[start,end] string	O (N)
sdscmp	Compare the size of two SDS	O (N)
Sdssplitlen	Cuts the given string s by a given Sep delimited string	O (N)

Redis source reading-sds string source reading