概述

简单动态字符串（SDS, Simple Dynamic String）是 Redis 底层所使用的的字符串表示（而不是使用传统的 C 字符串）。
redis需要的不仅仅是一个字符串变量，而是一个可以被修改的字符串值，我们设置的所有键值基本都是 SDS。

SDS结构体

typedef char *sds;struct sdshdr {// 记录 buf 数组中已使用字节的数量// 等于 SDS 所保存字符串的长度int len;// 记录 buf 数组中未使用字节的数量int free;// 字节数组，用于保存字符串char buf[];
};

知识点学习

SDS概述

SDS 遵循 C 字符串以空字符结尾的惯例， 保存空字符的 1 字节空间不计算在 SDS 的 len 属性里面，并且为空字符分配额外的 1 字节空间，以及添加空字符到字符串末尾等操作都是由 SDS 函数自动完成的，所以这个空字符对于 SDS 的使用者来说是完全透明的。遵循空字符结尾这一惯例的好处是， SDS 可以直接重用一部分 C 字符串函数库里面的函数。
SDS的优点如下:
1. 常数复杂度获取字符串长度
2. 杜绝缓冲区溢出
3. 减少修改字符串长度所需的内存重分配次数
4. 二进制安全
5. 兼容部分C字符串函数

SDS 与 C 字符串的区别

1. 常数复杂度获取字符串长度

C 字符串并不记录自身的长度信息， 所以为了获取一个 C 字符串的长度，程序必须遍历整个字符串，对遇到的每个字符进行计数，直到遇到代表字符串结尾的空字符为止， **这个操作的复杂度为 O(N) **。
程序只要访问 SDS 的 len 属性，就可以立即知道 SDS 的长度。SDS 将获取字符串长度所需的复杂度从 O(N) 降低到了 O(1) ，设置和更新 SDS 长度的工作是由 SDS 的 API 在执行时自动完成的，使用 SDS 无须进行任何手动修改长度的工作。

2. 杜绝缓冲区溢出

C 字符串不记录自身长度带来的一个问题是容易造成缓冲区溢出（buffer overflow）。例如：<string.h>/strcat 函数可以将 src 字符串中的内容拼接到 dest 字符串的末尾。当长度不足时会覆盖掉后面的。

SDS 的空间分配策略完全杜绝了发生缓冲区溢出的可能性：当 SDS API 需要对 SDS 进行修改时， API 会先检查 SDS 的空间是否满足修改所需的要求，如果不满足的话， API 会自动将 SDS 的空间扩展至执行修改所需的大小，然后才执行实际的修改操作，所以使用 SDS 既不需要手动修改 SDS 的空间大小，也不会出现前面所说的缓冲区溢出问题。

3. 减少修改字符串时带来的内存重分配次数

C 字符串并不记录自身的长度， C 字符串的底层实现总是一个 N+1 个字符长的数组（额外的一个字符空间用于保存空字符）。所以每次增长或者缩短一个 C 字符串， 程序都总要对保存这个 C 字符串的数组进行一次内存重分配操作。
为了避免 C 字符串的这种缺陷， SDS 通过未使用空间解除了字符串长度和底层数组长度之间的关联：在 SDS 中， buf 数组的长度不一定就是字符数量加一，数组里面可以包含未使用的字节，而这些字节的数量就由 SDS 的 free 属性记录。

通过未使用空间， SDS 实现了空间预分配和惰性空间释放两种优化策略。

空间预分配

空间预分配用于优化 SDS 的字符串增长操作：当 SDS 的 API 对一个 SDS 进行修改，并且需要对 SDS 进行空间扩展的时候，程序不仅会为 SDS 分配修改所必须要的空间，还会为 SDS 分配额外的未使用空间。
通过空间预分配策略， Redis 可以减少连续执行字符串增长操作所需的内存重分配次数。
SDS字符串分配策略：

拼接后的字符串长度不超过1M，分配两倍的内存
拼接够的字符串长度超过1M，多分配1M的内存 (字符串最大长度为 512M)

惰性空间释放策略

惰性空间释放用于优化 SDS 的字符串缩短操作：当 SDS 的 API 需要缩短 SDS 保存的字符串时，程序并不立即使用内存重分配来回收缩短后多出来的字节，而是使用 free 属性将这些字节的数量记录起来，并等待将来使用。

4. 二进制安全

C 字符串中的字符必须符合某种编码（比如 ASCII），并且除了字符串的末尾之外，字符串里面不能包含空字符，否则最先被程序读入的空字符将被误认为是字符串结尾 —— 这些限制使得 C 字符串只能保存文本数据，而不能保存像图片、音频、视频、压缩文件这样的二进制数据。

SDS 的 API 都是二进制安全的（binary-safe）：所有 SDS API 都会以处理二进制的方式来处理 SDS 存放在 buf 数组里的数据，程序不会对其中的数据做任何限制、过滤、或者假设 —— 数据在写入时是什么样的，它被读取时就是什么样。这也是我们将 SDS 的 buf 属性称为字节数组的原因 —— Redis 不是用这个数组来保存字符，而是用它来保存一系列二进制数据。

通过使用二进制安全的 SDS ，而不是 C 字符串，使得 Redis 不仅可以保存文本数据，还可以保存任意格式的二进制数据。

5.兼容部分 C 字符串函数

SDS 的 API 都是二进制安全的，但它们一样遵循 C 字符串以空字符结尾的惯例：这些 API 总会将 SDS 保存的数据的末尾设置为空字符，并且总会在为 buf 数组分配空间时多分配一个字节来容纳这个空字符， 这是为了让那些保存文本数据的 SDS 可以重用一部分 <string.h> 库定义的函数。

总结

C 字符串	SDS
获取字符串长度的复杂度为 O(N) 。	获取字符串长度的复杂度为 O(1) 。
API 是不安全的，可能会造成缓冲区溢出。	API 是安全的，不会造成缓冲区溢出。
修改字符串长度 N 次必然需要执行 N 次内存重分配。	修改字符串长度 N 次最多需要执行 N 次内存重分配。
只能保存文本数据。	可以保存文本或者二进制数据。
可以使用所有 <string.h> 库中的函数。	可以使用一部分 <string.h> 库中的函数。

代码实现

sds.h

/* SDSLib, A C dynamic strings library** Copyright (c) 2006-2010, Salvatore Sanfilippo <antirez at gmail dot com>* All rights reserved.** Redistribution and use in source and binary forms, with or without* modification, are permitted provided that the following conditions are met:**   * Redistributions of source code must retain the above copyright notice,*     this list of conditions and the following disclaimer.*   * Redistributions in binary form must reproduce the above copyright*     notice, this list of conditions and the following disclaimer in the*     documentation and/or other materials provided with the distribution.*   * Neither the name of Redis nor the names of its contributors may be used*     to endorse or promote products derived from this software without*     specific prior written permission.** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE* POSSIBILITY OF SUCH DAMAGE.*/#ifndef __SDS_H
#define __SDS_H/** 最大预分配长度*/
#define SDS_MAX_PREALLOC (1024*I1024)#include <sys/types.h>
#include <stdarg.h>/** 类型别名，用于指向 sdshdr 的 buf 属性*/
typedef char *sds;/** 保存字符串对象的结构*/
struct sdshdr {// buf 中已占用空间的长度int len;// buf 中剩余可用空间的长度int free;// 数据空间char buf[];
};/** 返回 sds 实际保存的字符串的长度** T = O(1)*/
static inline size_t sdslen(const sds s) {struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));return sh->len;
}/** 返回 sds 可用空间的长度** T = O(1)*/
static inline size_t sdsavail(const sds s) {struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));return sh->free;
}
//初始化字符串内存空间 如果传入值为空指针 不初始化分配的内存
sds sdsnewlen(const void *init, size_t initlen);
//初始化创建一个 长度为 传入字符串的 sds 长度为  buf的长度为传入字符串的长度 未使用空间为0
sds sdsnew(const char *init);
//初始化 空的 初始长度为0的字符串
sds sdsempty(void);
size_t sdslen(const sds s);
//根据给定的sds再去 创建copy一份一样的
sds sdsdup(const sds s);
void sdsfree(sds s);
//返回 sds 可用空间的长度
size_t sdsavail(const sds s);
//将 sds 扩充至指定长度，未使用的空间以 0 字节填充。
sds sdsgrowzero(sds s, size_t len);
//将长度为 len 的字符串 t 追加到 sds 的字符串末尾
sds sdscatlen(sds s, const void *t, size_t len);
//将给定字符串 t 追加到 sds 的末尾
sds sdscat(sds s, const char *t);
//相当于cat追加字符串
sds sdscatsds(sds s, const sds t);
//将字符串 t 的前 len 个字符复制到 sds s 当中，
sds sdscpylen(sds s, const char *t, size_t len);
// 将字符串复制到 sds 当中，
sds sdscpy(sds s, const char *t);sds sdscatvprintf(sds s, const char *fmt, va_list ap);
#ifdef __GNUC__
sds sdscatprintf(sds s, const char *fmt, ...)__attribute__((format(printf, 2, 3)));
#else
sds sdscatprintf(sds s, const char *fmt, ...);
#endif
//一部分格式化语义
sds sdscatfmt(sds s, char const *fmt, ...);
//可以剔除sds中指定的字符:
sds sdstrim(sds s, const char *cset);
void sdsrange(sds s, int start, int end);
void sdsupdatelen(sds s);
void sdsclear(sds s);
int sdscmp(const sds s1, const sds s2);
sds *sdssplitlen(const char *s, int len, const char *sep, int seplen, int *count);
void sdsfreesplitres(sds *tokens, int count);
void sdstolower(sds s);
void sdstoupper(sds s);
sds sdsfromlonglong(long long value);
sds sdscatrepr(sds s, const char *p, size_t len);
sds *sdssplitargs(const char *line, int *argc);
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen);
sds sdsjoin(char **argv, int argc, char *sep);/* Low level functions exposed to the user API */
sds sdsMakeRoomFor(sds s, size_t addlen);
void sdsIncrLen(sds s, int incr);
sds sdsRemoveFreeSpace(sds s);
size_t sdsAllocSize(sds s);#endif

sds.c

/* SDSLib, A C dynamic strings library** Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez at gmail dot com>* All rights reserved.** Redistribution and use in source and binary forms, with or without* modification, are permitted provided that the following conditions are met:**   * Redistributions of source code must retain the above copyright notice,*     this list of conditions and the following disclaimer.*   * Redistributions in binary form must reproduce the above copyright*     notice, this list of conditions and the following disclaimer in the*     documentation and/or other materials provided with the distribution.*   * Neither the name of Redis nor the names of its contributors may be used*     to endorse or promote products derived from this software without*     specific prior written permission.** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE* POSSIBILITY OF SUCH DAMAGE.*/#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include "sds.h"
#include "zmalloc.h"/** 根据给定的初始化字符串 init 和字符串长度 initlen* 创建一个新的 sds** 参数*  init ：初始化字符串指针*  initlen ：初始化字符串的长度** 返回值*  sds ：创建成功返回 sdshdr 相对应的 sds*        创建失败返回 NULL** 复杂度*  T = O(N)*/
/* Create a new sds string with the content specified by the 'init' pointer* and 'initlen'.* If NULL is used for 'init' the string is initialized with zero bytes.** The string is always null-termined (all the sds strings are, always) so* even if you create an sds string with:** mystring = sdsnewlen("abc",3");** You can print the string with printf() as there is an implicit \0 at the* end of the string. However the string is binary safe and can contain* \0 characters in the middle, as the length is stored in the sds header. */
sds sdsnewlen(const void *init, size_t initlen) {struct sdshdr *sh;// 根据是否有初始化内容，选择适当的内存分配方式// T = O(N)if (init) {// zmalloc 不初始化所分配的内存sh = zmalloc(sizeof(struct sdshdr)+initlen+1);} else {// zcalloc 将分配的内存全部初始化为 0sh = zcalloc(sizeof(struct sdshdr)+initlen+1);}// 内存分配失败，返回if (sh == NULL) return NULL;// 设置初始化长度sh->len = initlen;// 新 sds 不预留任何空间sh->free = 0;// 如果有指定初始化内容，将它们复制到 sdshdr 的 buf 中// T = O(N)if (initlen && init)memcpy(sh->buf, init, initlen);// 以 \0 结尾sh->buf[initlen] = '\0';// 返回 buf 部分，而不是整个 sdshdrreturn (char*)sh->buf;
}/** 创建并返回一个只保存了空字符串 "" 的 sds** 返回值*  sds ：创建成功返回 sdshdr 相对应的 sds*        创建失败返回 NULL** 复杂度*  T = O(1)*/
/* Create an empty (zero length) sds string. Even in this case the string* always has an implicit null term. */
sds sdsempty(void) {return sdsnewlen("",0);
}/** 根据给定字符串 init ，创建一个包含同样字符串的 sds** 参数*  init ：如果输入为 NULL ，那么创建一个空白 sds*         否则，新创建的 sds 中包含和 init 内容相同字符串** 返回值*  sds ：创建成功返回 sdshdr 相对应的 sds*        创建失败返回 NULL** 复杂度*  T = O(N)*/
/* Create a new sds string starting from a null termined C string. */
sds sdsnew(const char *init) {size_t initlen = (init == NULL) ? 0 : strlen(init);return sdsnewlen(init, initlen);
}/** 复制给定 sds 的副本** 返回值*  sds ：创建成功返回输入 sds 的副本*        创建失败返回 NULL** 复杂度*  T = O(N)*/
/* Duplicate an sds string. */
sds sdsdup(const sds s) {return sdsnewlen(s, sdslen(s));
}/** 释放给定的 sds** 复杂度*  T = O(N)*/
/* Free an sds string. No operation is performed if 's' is NULL. */
void sdsfree(sds s) {if (s == NULL) return;zfree(s-sizeof(struct sdshdr));
}// 未使用函数，可能已废弃
/* Set the sds string length to the length as obtained with strlen(), so* considering as content only up to the first null term character.** This function is useful when the sds string is hacked manually in some* way, like in the following example:** s = sdsnew("foobar");* s[2] = '\0';* sdsupdatelen(s);* printf("%d\n", sdslen(s));** The output will be "2", but if we comment out the call to sdsupdatelen()* the output will be "6" as the string was modified but the logical length* remains 6 bytes. */
void sdsupdatelen(sds s) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));int reallen = strlen(s);sh->free += (sh->len-reallen);sh->len = reallen;
}/** 在不释放 SDS 的字符串空间的情况下，* 重置 SDS 所保存的字符串为空字符串。** 复杂度*  T = O(1)*/
/* Modify an sds string on-place to make it empty (zero length).* However all the existing buffer is not discarded but set as free space* so that next append operations will not require allocations up to the* number of bytes previously available. */
void sdsclear(sds s) {// 取出 sdshdrstruct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));// 重新计算属性sh->free += sh->len;sh->len = 0;// 将结束符放到最前面（相当于惰性地删除 buf 中的内容）sh->buf[0] = '\0';
}/* Enlarge the free space at the end of the sds string so that the caller* is sure that after calling this function can overwrite up to addlen* bytes after the end of the string, plus one more byte for nul term.* * Note: this does not change the *length* of the sds string as returned* by sdslen(), but only the free buffer space we have. */
/** 对 sds 中 buf 的长度进行扩展，确保在函数执行之后，* buf 至少会有 addlen + 1 长度的空余空间* （额外的 1 字节是为 \0 准备的）** 返回值*  sds ：扩展成功返回扩展后的 sds*        扩展失败返回 NULL** 复杂度*  T = O(N)*/
sds sdsMakeRoomFor(sds s, size_t addlen) {struct sdshdr *sh, *newsh;// 获取 s 目前的空余空间长度size_t free = sdsavail(s);size_t len, newlen;// s 目前的空余空间已经足够，无须再进行扩展，直接返回if (free >= addlen) return s;// 获取 s 目前已占用空间的长度len = sdslen(s);sh = (void*) (s-(sizeof(struct sdshdr)));// s 最少需要的长度newlen = (len+addlen);// 根据新长度，为 s 分配新空间所需的大小if (newlen < SDS_MAX_PREALLOC)// 如果新长度小于 SDS_MAX_PREALLOC // 那么为它分配两倍于所需长度的空间newlen *= 2;else// 否则，分配长度为目前长度加上 SDS_MAX_PREALLOCnewlen += SDS_MAX_PREALLOC;// T = O(N)newsh = zrealloc(sh, sizeof(struct sdshdr)+newlen+1);// 内存不足，分配失败，返回if (newsh == NULL) return NULL;// 更新 sds 的空余长度newsh->free = newlen - len;// 返回 sdsreturn newsh->buf;
}/** 回收 sds 中的空闲空间，* 回收不会对 sds 中保存的字符串内容做任何修改。** 返回值*  sds ：内存调整后的 sds** 复杂度*  T = O(N)*/
/* Reallocate the sds string so that it has no free space at the end. The* contained string remains not altered, but next concatenation operations* will require a reallocation.** After the call, the passed sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call. */
sds sdsRemoveFreeSpace(sds s) {struct sdshdr *sh;sh = (void*) (s-(sizeof(struct sdshdr)));// 进行内存重分配，让 buf 的长度仅仅足够保存字符串内容// T = O(N)sh = zrealloc(sh, sizeof(struct sdshdr)+sh->len+1);// 空余空间为 0sh->free = 0;return sh->buf;
}/** 返回给定 sds 分配的内存字节数** 复杂度*  T = O(1)*/
/* Return the total size of the allocation of the specifed sds string,* including:* 1) The sds header before the pointer.* 2) The string.* 3) The free buffer at the end if any.* 4) The implicit null term.*/
size_t sdsAllocSize(sds s) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));return sizeof(*sh)+sh->len+sh->free+1;
}/* Increment the sds length and decrements the left free space at the* end of the string according to 'incr'. Also set the null term* in the new end of the string.** 根据 incr 参数，增加 sds 的长度，缩减空余空间，* 并将 \0 放到新字符串的尾端** This function is used in order to fix the string length after the* user calls sdsMakeRoomFor(), writes something after the end of* the current string, and finally needs to set the new length.** 这个函数是在调用 sdsMakeRoomFor() 对字符串进行扩展，* 然后用户在字符串尾部写入了某些内容之后，* 用来正确更新 free 和 len 属性的。** Note: it is possible to use a negative increment in order to* right-trim the string.** 如果 incr 参数为负数，那么对字符串进行右截断操作。** Usage example:** Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the* following schema, to cat bytes coming from the kernel to the end of an* sds string without copying into an intermediate buffer:** 以下是 sdsIncrLen 的用例：** oldlen = sdslen(s);* s = sdsMakeRoomFor(s, BUFFER_SIZE);* nread = read(fd, s+oldlen, BUFFER_SIZE);* ... check for nread <= 0 and handle it ...* sdsIncrLen(s, nread);** 复杂度*  T = O(1)*/
void sdsIncrLen(sds s, int incr) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));// 确保 sds 空间足够assert(sh->free >= incr);// 更新属性sh->len += incr;sh->free -= incr;// 这个 assert 其实可以忽略// 因为前一个 assert 已经确保 sh->free - incr >= 0 了assert(sh->free >= 0);// 放置新的结尾符号s[sh->len] = '\0';
}/* Grow the sds to have the specified length. Bytes that were not part of* the original length of the sds will be set to zero.** if the specified length is smaller than the current length, no operation* is performed. */
/** 将 sds 扩充至指定长度，未使用的空间以 0 字节填充。** 返回值*  sds ：扩充成功返回新 sds ，失败返回 NULL** 复杂度：*  T = O(N)*/
sds sdsgrowzero(sds s, size_t len) {struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));size_t totlen, curlen = sh->len;// 如果 len 比字符串的现有长度小，// 那么直接返回，不做动作if (len <= curlen) return s;// 扩展 sds// T = O(N)s = sdsMakeRoomFor(s,len-curlen);// 如果内存不足，直接返回if (s == NULL) return NULL;/* Make sure added region doesn't contain garbage */// 将新分配的空间用 0 填充，防止出现垃圾内容// T = O(N)sh = (void*)(s-(sizeof(struct sdshdr)));memset(s+curlen,0,(len-curlen+1)); /* also set trailing \0 byte */// 更新属性totlen = sh->len+sh->free;sh->len = len;sh->free = totlen-sh->len;// 返回新的 sdsreturn s;
}/** 将长度为 len 的字符串 t 追加到 sds 的字符串末尾** 返回值*  sds ：追加成功返回新 sds ，失败返回 NULL** 复杂度*  T = O(N)*/
/* Append the specified binary-safe string pointed by 't' of 'len' bytes to the* end of the specified sds string 's'.** After the call, the passed sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call. */
sds sdscatlen(sds s, const void *t, size_t len) {struct sdshdr *sh;// 原有字符串长度size_t curlen = sdslen(s);// 扩展 sds 空间// T = O(N)s = sdsMakeRoomFor(s,len);// 内存不足？直接返回if (s == NULL) return NULL;// 复制 t 中的内容到字符串后部// T = O(N)sh = (void*) (s-(sizeof(struct sdshdr)));memcpy(s+curlen, t, len);// 更新属性sh->len = curlen+len;sh->free = sh->free-len;// 添加新结尾符号s[curlen+len] = '\0';// 返回新 sdsreturn s;
}/** 将给定字符串 t 追加到 sds 的末尾* * 返回值*  sds ：追加成功返回新 sds ，失败返回 NULL** 复杂度*  T = O(N)*/
/* Append the specified null termianted C string to the sds string 's'.** After the call, the passed sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call. */
sds sdscat(sds s, const char *t) {return sdscatlen(s, t, strlen(t));
}/** 将另一个 sds 追加到一个 sds 的末尾* * 返回值*  sds ：追加成功返回新 sds ，失败返回 NULL** 复杂度*  T = O(N)*/
/* Append the specified sds 't' to the existing sds 's'.** After the call, the modified sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call. */
sds sdscatsds(sds s, const sds t) {return sdscatlen(s, t, sdslen(t));
}/** 将字符串 t 的前 len 个字符复制到 sds s 当中，* 并在字符串的最后添加终结符。** 如果 sds 的长度少于 len 个字符，那么扩展 sds** 复杂度*  T = O(N)** 返回值*  sds ：复制成功返回新的 sds ，否则返回 NULL*/
/* Destructively modify the sds string 's' to hold the specified binary* safe string pointed by 't' of length 'len' bytes. */
sds sdscpylen(sds s, const char *t, size_t len) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));// sds 现有 buf 的长度size_t totlen = sh->free+sh->len;// 如果 s 的 buf 长度不满足 len ，那么扩展它if (totlen < len) {// T = O(N)s = sdsMakeRoomFor(s,len-sh->len);if (s == NULL) return NULL;sh = (void*) (s-(sizeof(struct sdshdr)));totlen = sh->free+sh->len;}// 复制内容// T = O(N)memcpy(s, t, len);// 添加终结符号s[len] = '\0';// 更新属性sh->len = len;sh->free = totlen-len;// 返回新的 sdsreturn s;
}/** 将字符串复制到 sds 当中，* 覆盖原有的字符。** 如果 sds 的长度少于字符串的长度，那么扩展 sds 。** 复杂度*  T = O(N)** 返回值*  sds ：复制成功返回新的 sds ，否则返回 NULL*/
/* Like sdscpylen() but 't' must be a null-termined string so that the length* of the string is obtained with strlen(). */
sds sdscpy(sds s, const char *t) {return sdscpylen(s, t, strlen(t));
}/* Helper for sdscatlonglong() doing the actual number -> string* conversion. 's' must point to a string with room for at least* SDS_LLSTR_SIZE bytes.** The function returns the lenght of the null-terminated string* representation stored at 's'. */
#define SDS_LLSTR_SIZE 21
int sdsll2str(char *s, long long value) {char *p, aux;unsigned long long v;size_t l;/* Generate the string representation, this method produces* an reversed string. */v = (value < 0) ? -value : value;p = s;do {*p++ = '0'+(v%10);v /= 10;} while(v);if (value < 0) *p++ = '-';/* Compute length and add null term. */l = p-s;*p = '\0';/* Reverse the string. */p--;while(s < p) {aux = *s;*s = *p;*p = aux;s++;p--;}return l;
}/* Identical sdsll2str(), but for unsigned long long type. */
int sdsull2str(char *s, unsigned long long v) {char *p, aux;size_t l;/* Generate the string representation, this method produces* an reversed string. */p = s;do {*p++ = '0'+(v%10);v /= 10;} while(v);/* Compute length and add null term. */l = p-s;*p = '\0';/* Reverse the string. */p--;while(s < p) {aux = *s;*s = *p;*p = aux;s++;p--;}return l;
}/* Create an sds string from a long long value. It is much faster than:** sdscatprintf(sdsempty(),"%lld\n", value);*/
// 根据输入的 long long 值 value ，创建一个 SDS
sds sdsfromlonglong(long long value) {char buf[SDS_LLSTR_SIZE];int len = sdsll2str(buf,value);return sdsnewlen(buf,len);
}/* * 打印函数，被 sdscatprintf 所调用** T = O(N^2)*/
/* Like sdscatpritf() but gets va_list instead of being variadic. */
sds sdscatvprintf(sds s, const char *fmt, va_list ap) {va_list cpy;char staticbuf[1024], *buf = staticbuf, *t;size_t buflen = strlen(fmt)*2;/* We try to start using a static buffer for speed.* If not possible we revert to heap allocation. */if (buflen > sizeof(staticbuf)) {buf = zmalloc(buflen);if (buf == NULL) return NULL;} else {buflen = sizeof(staticbuf);}/* Try with buffers two times bigger every time we fail to* fit the string in the current buffer size. */while(1) {buf[buflen-2] = '\0';va_copy(cpy,ap);// T = O(N)vsnprintf(buf, buflen, fmt, cpy);if (buf[buflen-2] != '\0') {if (buf != staticbuf) zfree(buf);buflen *= 2;buf = zmalloc(buflen);if (buf == NULL) return NULL;continue;}break;}/* Finally concat the obtained string to the SDS string and return it. */t = sdscat(s, buf);if (buf != staticbuf) zfree(buf);return t;
}/** 打印任意数量个字符串，并将这些字符串追加到给定 sds 的末尾** T = O(N^2)*/
/* Append to the sds string 's' a string obtained using printf-alike format* specifier.** After the call, the modified sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call.** Example:** s = sdsempty("Sum is: ");* s = sdscatprintf(s,"%d+%d = %d",a,b,a+b).** Often you need to create a string from scratch with the printf-alike* format. When this is the need, just use sdsempty() as the target string:** s = sdscatprintf(sdsempty(), "... your format ...", args);*/
sds sdscatprintf(sds s, const char *fmt, ...) {va_list ap;char *t;va_start(ap, fmt);// T = O(N^2)t = sdscatvprintf(s,fmt,ap);va_end(ap);return t;
}/* This function is similar to sdscatprintf, but much faster as it does* not rely on sprintf() family functions implemented by the libc that* are often very slow. Moreover directly handling the sds string as* new data is concatenated provides a performance improvement.** However this function only handles an incompatible subset of printf-alike* format specifiers:** %s - C String* %S - SDS string* %i - signed int* %I - 64 bit signed integer (long long, int64_t)* %u - unsigned int* %U - 64 bit unsigned integer (unsigned long long, uint64_t)* %% - Verbatim "%" character.*/
sds sdscatfmt(sds s, char const *fmt, ...) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));size_t initlen = sdslen(s);const char *f = fmt;int i;va_list ap;va_start(ap,fmt);f = fmt;    /* Next format specifier byte to process. */i = initlen; /* Position of the next byte to write to dest str. */while(*f) {char next, *str;size_t l;long long num;unsigned long long unum;/* Make sure there is always space for at least 1 char. */if (sh->free == 0) {s = sdsMakeRoomFor(s,1);sh = (void*) (s-(sizeof(struct sdshdr)));}switch(*f) {case '%':next = *(f+1);f++;switch(next) {case 's':case 'S':str = va_arg(ap,char*);l = (next == 's') ? strlen(str) : sdslen(str);if (sh->free < l) {s = sdsMakeRoomFor(s,l);sh = (void*) (s-(sizeof(struct sdshdr)));}memcpy(s+i,str,l);sh->len += l;sh->free -= l;i += l;break;case 'i':case 'I':if (next == 'i')num = va_arg(ap,int);elsenum = va_arg(ap,long long);{char buf[SDS_LLSTR_SIZE];l = sdsll2str(buf,num);if (sh->free < l) {s = sdsMakeRoomFor(s,l);sh = (void*) (s-(sizeof(struct sdshdr)));}memcpy(s+i,buf,l);sh->len += l;sh->free -= l;i += l;}break;case 'u':case 'U':if (next == 'u')unum = va_arg(ap,unsigned int);elseunum = va_arg(ap,unsigned long long);{char buf[SDS_LLSTR_SIZE];l = sdsull2str(buf,unum);if (sh->free < l) {s = sdsMakeRoomFor(s,l);sh = (void*) (s-(sizeof(struct sdshdr)));}memcpy(s+i,buf,l);sh->len += l;sh->free -= l;i += l;}break;default: /* Handle %% and generally %<unknown>. */s[i++] = next;sh->len += 1;sh->free -= 1;break;}break;default:s[i++] = *f;sh->len += 1;sh->free -= 1;break;}f++;}va_end(ap);/* Add null-term */s[i] = '\0';return s;
}/** 对 sds 左右两端进行修剪，清除其中 cset 指定的所有字符** 比如 sdsstrim(xxyyabcyyxy, "xy") 将返回 "abc"** 复杂性：*  T = O(M*N)，M 为 SDS 长度， N 为 cset 长度。*/
/* Remove the part of the string from left and from right composed just of* contiguous characters found in 'cset', that is a null terminted C string.** After the call, the modified sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call.** Example:** s = sdsnew("AA...AA.a.aa.aHelloWorld     :::");* s = sdstrim(s,"A. :");* printf("%s\n", s);** Output will be just "Hello World".*/
sds sdstrim(sds s, const char *cset) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));char *start, *end, *sp, *ep;size_t len;// 设置和记录指针sp = start = s;ep = end = s+sdslen(s)-1;// 修剪, T = O(N^2)while(sp <= end && strchr(cset, *sp)) sp++;while(ep > start && strchr(cset, *ep)) ep--;// 计算 trim 完毕之后剩余的字符串长度len = (sp > ep) ? 0 : ((ep-sp)+1);// 如果有需要，前移字符串内容// T = O(N)if (sh->buf != sp) memmove(sh->buf, sp, len);// 添加终结符sh->buf[len] = '\0';// 更新属性sh->free = sh->free+(sh->len-len);sh->len = len;// 返回修剪后的 sdsreturn s;
}/** 按索引对截取 sds 字符串的其中一段* start 和 end 都是闭区间（包含在内）** 索引从 0 开始，最大为 sdslen(s) - 1* 索引可以是负数， sdslen(s) - 1 == -1** 复杂度*  T = O(N)*/
/* Turn the string into a smaller (or equal) string containing only the* substring specified by the 'start' and 'end' indexes.** start and end can be negative, where -1 means the last character of the* string, -2 the penultimate character, and so forth.** The interval is inclusive, so the start and end characters will be part* of the resulting string.** The string is modified in-place.** Example:** s = sdsnew("Hello World");* sdsrange(s,1,-1); => "ello World"*/
void sdsrange(sds s, int start, int end) {struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));size_t newlen, len = sdslen(s);if (len == 0) return;if (start < 0) {start = len+start;if (start < 0) start = 0;}if (end < 0) {end = len+end;if (end < 0) end = 0;}newlen = (start > end) ? 0 : (end-start)+1;if (newlen != 0) {if (start >= (signed)len) {newlen = 0;} else if (end >= (signed)len) {end = len-1;newlen = (start > end) ? 0 : (end-start)+1;}} else {start = 0;}// 如果有需要，对字符串进行移动// T = O(N)if (start && newlen) memmove(sh->buf, sh->buf+start, newlen);// 添加终结符sh->buf[newlen] = 0;// 更新属性sh->free = sh->free+(sh->len-newlen);sh->len = newlen;
}/** 将 sds 字符串中的所有字符转换为小写** T = O(N)*/
/* Apply tolower() to every character of the sds string 's'. */
void sdstolower(sds s) {int len = sdslen(s), j;for (j = 0; j < len; j++) s[j] = tolower(s[j]);
}/** 将 sds 字符串中的所有字符转换为大写** T = O(N)*/
/* Apply toupper() to every character of the sds string 's'. */
void sdstoupper(sds s) {int len = sdslen(s), j;for (j = 0; j < len; j++) s[j] = toupper(s[j]);
}/** 对比两个 sds ， strcmp 的 sds 版本** 返回值*  int ：相等返回 0 ，s1 较大返回正数， s2 较大返回负数** T = O(N)*/
/* Compare two sds strings s1 and s2 with memcmp().** Return value:**     1 if s1 > s2.*    -1 if s1 < s2.*     0 if s1 and s2 are exactly the same binary string.** If two strings share exactly the same prefix, but one of the two has* additional characters, the longer string is considered to be greater than* the smaller one. */
int sdscmp(const sds s1, const sds s2) {size_t l1, l2, minlen;int cmp;l1 = sdslen(s1);l2 = sdslen(s2);minlen = (l1 < l2) ? l1 : l2;cmp = memcmp(s1,s2,minlen);if (cmp == 0) return l1-l2;return cmp;
}/* Split 's' with separator in 'sep'. An array* of sds strings is returned. *count will be set* by reference to the number of tokens returned.** 使用分隔符 sep 对 s 进行分割，返回一个 sds 字符串的数组。* *count 会被设置为返回数组元素的数量。** On out of memory, zero length string, zero length* separator, NULL is returned.** 如果出现内存不足、字符串长度为 0 或分隔符长度为 0* 的情况，返回 NULL** Note that 'sep' is able to split a string using* a multi-character separator. For example* sdssplit("foo_-_bar","_-_"); will return two* elements "foo" and "bar".** 注意分隔符可以的是包含多个字符的字符串** This version of the function is binary-safe but* requires length arguments. sdssplit() is just the* same function but for zero-terminated strings.** 这个函数接受 len 参数，因此它是二进制安全的。* （文档中提到的 sdssplit() 已废弃）** T = O(N^2)*/
sds *sdssplitlen(const char *s, int len, const char *sep, int seplen, int *count) {int elements = 0, slots = 5, start = 0, j;sds *tokens;if (seplen < 1 || len < 0) return NULL;tokens = zmalloc(sizeof(sds)*slots);if (tokens == NULL) return NULL;if (len == 0) {*count = 0;return tokens;}// T = O(N^2)for (j = 0; j < (len-(seplen-1)); j++) {/* make sure there is room for the next element and the final one */if (slots < elements+2) {sds *newtokens;slots *= 2;newtokens = zrealloc(tokens,sizeof(sds)*slots);if (newtokens == NULL) goto cleanup;tokens = newtokens;}/* search the separator */// T = O(N)if ((seplen == 1 && *(s+j) == sep[0]) || (memcmp(s+j,sep,seplen) == 0)) {tokens[elements] = sdsnewlen(s+start,j-start);if (tokens[elements] == NULL) goto cleanup;elements++;start = j+seplen;j = j+seplen-1; /* skip the separator */}}/* Add the final element. We are sure there is room in the tokens array. */tokens[elements] = sdsnewlen(s+start,len-start);if (tokens[elements] == NULL) goto cleanup;elements++;*count = elements;return tokens;cleanup:{int i;for (i = 0; i < elements; i++) sdsfree(tokens[i]);zfree(tokens);*count = 0;return NULL;}
}/** 释放 tokens 数组中 count 个 sds** T = O(N^2)*/
/* Free the result returned by sdssplitlen(), or do nothing if 'tokens' is NULL. */
void sdsfreesplitres(sds *tokens, int count) {if (!tokens) return;while(count--)sdsfree(tokens[count]);zfree(tokens);
}/** 将长度为 len 的字符串 p 以带引号（quoted）的格式* 追加到给定 sds 的末尾** T = O(N)*/
/* Append to the sds string "s" an escaped string representation where* all the non-printable characters (tested with isprint()) are turned into* escapes in the form "\n\r\a...." or "\x<hex-number>".** After the call, the modified sds string is no longer valid and all the* references must be substituted with the new pointer returned by the call. */
sds sdscatrepr(sds s, const char *p, size_t len) {s = sdscatlen(s,"\"",1);while(len--) {switch(*p) {case '\\':case '"':s = sdscatprintf(s,"\\%c",*p);break;case '\n': s = sdscatlen(s,"\\n",2); break;case '\r': s = sdscatlen(s,"\\r",2); break;case '\t': s = sdscatlen(s,"\\t",2); break;case '\a': s = sdscatlen(s,"\\a",2); break;case '\b': s = sdscatlen(s,"\\b",2); break;default:if (isprint(*p))s = sdscatprintf(s,"%c",*p);elses = sdscatprintf(s,"\\x%02x",(unsigned char)*p);break;}p++;}return sdscatlen(s,"\"",1);
}/* Helper function for sdssplitargs() that returns non zero if 'c'* is a valid hex digit. */
/** 如果 c 为十六进制符号的其中一个，返回正数** T = O(1)*/
int is_hex_digit(char c) {return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') ||(c >= 'A' && c <= 'F');
}/* Helper function for sdssplitargs() that converts a hex digit into an* integer from 0 to 15 */
/** 将十六进制符号转换为 10 进制** T = O(1)*/
int hex_digit_to_int(char c) {switch(c) {case '0': return 0;case '1': return 1;case '2': return 2;case '3': return 3;case '4': return 4;case '5': return 5;case '6': return 6;case '7': return 7;case '8': return 8;case '9': return 9;case 'a': case 'A': return 10;case 'b': case 'B': return 11;case 'c': case 'C': return 12;case 'd': case 'D': return 13;case 'e': case 'E': return 14;case 'f': case 'F': return 15;default: return 0;}
}/* Split a line into arguments, where every argument can be in the* following programming-language REPL-alike form:** 将一行文本分割成多个参数，每个参数可以有以下的类编程语言 REPL 格式：** foo bar "newline are supported\n" and "\xff\x00otherstuff"** The number of arguments is stored into *argc, and an array* of sds is returned.** 参数的个数会保存在 *argc 中，函数返回一个 sds 数组。** The caller should free the resulting array of sds strings with* sdsfreesplitres().** 调用者应该使用 sdsfreesplitres() 来释放函数返回的 sds 数组。** Note that sdscatrepr() is able to convert back a string into* a quoted string in the same format sdssplitargs() is able to parse.** sdscatrepr() 可以将一个字符串转换为一个带引号（quoted）的字符串，* 这个带引号的字符串可以被 sdssplitargs() 分析。** The function returns the allocated tokens on success, even when the* input string is empty, or NULL if the input contains unbalanced* quotes or closed quotes followed by non space characters* as in: "foo"bar or "foo'** 即使输入出现空字符串， NULL ，或者输入带有未对应的括号，* 函数都会将已成功处理的字符串先返回。** 这个函数主要用于 config.c 中对配置文件进行分析。* 例子：*  sds *arr = sdssplitargs("timeout 10086\r\nport 123321\r\n");* 会得出*  arr[0] = "timeout"*  arr[1] = "10086"*  arr[2] = "port"*  arr[3] = "123321"** T = O(N^2)*/
sds *sdssplitargs(const char *line, int *argc) {const char *p = line;char *current = NULL;char **vector = NULL;*argc = 0;while(1) {/* skip blanks */// 跳过空白// T = O(N)while(*p && isspace(*p)) p++;if (*p) {/* get a token */int inq=0;  /* set to 1 if we are in "quotes" */int insq=0; /* set to 1 if we are in 'single quotes' */int done=0;if (current == NULL) current = sdsempty();// T = O(N)while(!done) {if (inq) {if (*p == '\\' && *(p+1) == 'x' &&is_hex_digit(*(p+2)) &&is_hex_digit(*(p+3))){unsigned char byte;byte = (hex_digit_to_int(*(p+2))*16)+hex_digit_to_int(*(p+3));current = sdscatlen(current,(char*)&byte,1);p += 3;} else if (*p == '\\' && *(p+1)) {char c;p++;switch(*p) {case 'n': c = '\n'; break;case 'r': c = '\r'; break;case 't': c = '\t'; break;case 'b': c = '\b'; break;case 'a': c = '\a'; break;default: c = *p; break;}current = sdscatlen(current,&c,1);} else if (*p == '"') {/* closing quote must be followed by a space or* nothing at all. */if (*(p+1) && !isspace(*(p+1))) goto err;done=1;} else if (!*p) {/* unterminated quotes */goto err;} else {current = sdscatlen(current,p,1);}} else if (insq) {if (*p == '\\' && *(p+1) == '\'') {p++;current = sdscatlen(current,"'",1);} else if (*p == '\'') {/* closing quote must be followed by a space or* nothing at all. */if (*(p+1) && !isspace(*(p+1))) goto err;done=1;} else if (!*p) {/* unterminated quotes */goto err;} else {current = sdscatlen(current,p,1);}} else {switch(*p) {case ' ':case '\n':case '\r':case '\t':case '\0':done=1;break;case '"':inq=1;break;case '\'':insq=1;break;default:current = sdscatlen(current,p,1);break;}}if (*p) p++;}/* add the token to the vector */// T = O(N)vector = zrealloc(vector,((*argc)+1)*sizeof(char*));vector[*argc] = current;(*argc)++;current = NULL;} else {/* Even on empty input string return something not NULL. */if (vector == NULL) vector = zmalloc(sizeof(void*));return vector;}}err:while((*argc)--)sdsfree(vector[*argc]);zfree(vector);if (current) sdsfree(current);*argc = 0;return NULL;
}/* Modify the string substituting all the occurrences of the set of* characters specified in the 'from' string to the corresponding character* in the 'to' array.** 将字符串 s 中，* 所有在 from 中出现的字符，替换成 to 中的字符** For instance: sdsmapchars(mystring, "ho", "01", 2)* will have the effect of turning the string "hello" into "0ell1".** 比如调用 sdsmapchars(mystring, "ho", "01", 2)* 就会将 "hello" 转换为 "0ell1"** The function returns the sds string pointer, that is always the same* as the input pointer since no resize is needed. * 因为无须对 sds 进行大小调整，* 所以返回的 sds 输入的 sds 一样** T = O(N^2)*/
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {size_t j, i, l = sdslen(s);// 遍历输入字符串for (j = 0; j < l; j++) {// 遍历映射for (i = 0; i < setlen; i++) {// 替换字符串if (s[j] == from[i]) {s[j] = to[i];break;}}}return s;
}/* Join an array of C strings using the specified separator (also a C string).* Returns the result as an sds string. */
sds sdsjoin(char **argv, int argc, char *sep) {sds join = sdsempty();int j;for (j = 0; j < argc; j++) {join = sdscat(join, argv[j]);if (j != argc-1) join = sdscat(join,sep);}return join;
}#ifdef SDS_TEST_MAIN
#include <stdio.h>
#include "testhelp.h"
#include "limits.h"int main(void) {{struct sdshdr *sh;sds x = sdsnew("foo"), y;test_cond("Create a string and obtain the length",sdslen(x) == 3 && memcmp(x,"foo\0",4) == 0)sdsfree(x);x = sdsnewlen("foo",2);test_cond("Create a string with specified length",sdslen(x) == 2 && memcmp(x,"fo\0",3) == 0)x = sdscat(x,"bar");test_cond("Strings concatenation",sdslen(x) == 5 && memcmp(x,"fobar\0",6) == 0);x = sdscpy(x,"a");test_cond("sdscpy() against an originally longer string",sdslen(x) == 1 && memcmp(x,"a\0",2) == 0)x = sdscpy(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk");test_cond("sdscpy() against an originally shorter string",sdslen(x) == 33 &&memcmp(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk\0",33) == 0)sdsfree(x);x = sdscatprintf(sdsempty(),"%d",123);test_cond("sdscatprintf() seems working in the base case",sdslen(x) == 3 && memcmp(x,"123\0",4) == 0)sdsfree(x);x = sdsnew("--");x = sdscatfmt(x, "Hello %s World %I,%I--", "Hi!", LLONG_MIN,LLONG_MAX);test_cond("sdscatfmt() seems working in the base case",sdslen(x) == 60 &&memcmp(x,"--Hello Hi! World -9223372036854775808,""9223372036854775807--",60) == 0)sdsfree(x);x = sdsnew("--");x = sdscatfmt(x, "%u,%U--", UINT_MAX, ULLONG_MAX);test_cond("sdscatfmt() seems working with unsigned numbers",sdslen(x) == 35 &&memcmp(x,"--4294967295,18446744073709551615--",35) == 0)sdsfree(x);x = sdsnew("xxciaoyyy");sdstrim(x,"xy");test_cond("sdstrim() correctly trims characters",sdslen(x) == 4 && memcmp(x,"ciao\0",5) == 0)y = sdsdup(x);sdsrange(y,1,1);test_cond("sdsrange(...,1,1)",sdslen(y) == 1 && memcmp(y,"i\0",2) == 0)sdsfree(y);y = sdsdup(x);sdsrange(y,1,-1);test_cond("sdsrange(...,1,-1)",sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0)sdsfree(y);y = sdsdup(x);sdsrange(y,-2,-1);test_cond("sdsrange(...,-2,-1)",sdslen(y) == 2 && memcmp(y,"ao\0",3) == 0)sdsfree(y);y = sdsdup(x);sdsrange(y,2,1);test_cond("sdsrange(...,2,1)",sdslen(y) == 0 && memcmp(y,"\0",1) == 0)sdsfree(y);y = sdsdup(x);sdsrange(y,1,100);test_cond("sdsrange(...,1,100)",sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0)sdsfree(y);y = sdsdup(x);sdsrange(y,100,100);test_cond("sdsrange(...,100,100)",sdslen(y) == 0 && memcmp(y,"\0",1) == 0)sdsfree(y);sdsfree(x);x = sdsnew("foo");y = sdsnew("foa");test_cond("sdscmp(foo,foa)", sdscmp(x,y) > 0)sdsfree(y);sdsfree(x);x = sdsnew("bar");y = sdsnew("bar");test_cond("sdscmp(bar,bar)", sdscmp(x,y) == 0)sdsfree(y);sdsfree(x);x = sdsnew("aar");y = sdsnew("bar");test_cond("sdscmp(bar,bar)", sdscmp(x,y) < 0)sdsfree(y);sdsfree(x);x = sdsnewlen("\a\n\0foo\r",7);y = sdscatrepr(sdsempty(),x,sdslen(x));test_cond("sdscatrepr(...data...)",memcmp(y,"\"\\a\\n\\x00foo\\r\"",15) == 0){int oldfree;sdsfree(x);x = sdsnew("0");sh = (void*) (x-(sizeof(struct sdshdr)));test_cond("sdsnew() free/len buffers", sh->len == 1 && sh->free == 0);x = sdsMakeRoomFor(x,1);sh = (void*) (x-(sizeof(struct sdshdr)));test_cond("sdsMakeRoomFor()", sh->len == 1 && sh->free > 0);oldfree = sh->free;x[1] = '1';sdsIncrLen(x,1);test_cond("sdsIncrLen() -- content", x[0] == '0' && x[1] == '1');test_cond("sdsIncrLen() -- len", sh->len == 2);test_cond("sdsIncrLen() -- free", sh->free == oldfree-1);}}test_report()return 0;
}
#endif

redis源码学习-03_动态字符串SDS相关推荐

Redis源码阅读笔记-动态字符串(SDS)结构
2019独角兽企业重金招聘Python工程师标准>>> Redis中采用自定义的结构来保存字符串,在sds.h中: /* Note: sdshdr5 is never used, w ...
唯快不破：redis源码剖析04-sds动态字符串
阅读完redis动态字符串封装最大的一个感悟就是封装的优美,在原有char *字符串基础上添加了字符串头部元信息,这样既方便了字符串的管理,又不失原有的使用方便性.并且充分调用了c底层api高效进行字 ...
redis笔记_源码_简单动态字符串SDS
参照:https://zcheng.ren/sourcecodeanalysis/theannotatedredissourcesds/#sds%E5%B0%8F%E7%BB%93 这里用char b ...
redis源码学习笔记目录
Redis源码分析(零)学习路径笔记 Redis源码分析(一)redis.c //redis-server.c Redis源码分析(二)redis-cli.c Redis源码剖析(三)--基础数据结构 ...
Redis源码学习（20），学习感悟
最近学习Redis源码也有半个月的时间了,有不少收获也有不少感悟,今天来好好聊聊我学习的感悟. 1 发现问题人非圣贤孰能无过,只要是人难免会犯错,回顾我之前的学习历程,其实是可以发现不少的问 ...
【Redis学习笔记】2018-05-30 Redis源码学习之Ziplist、Server
作者:施洪宝顺风车运营研发团队一. 压缩列表压缩列表是Redis的关键数据结构之一.目前已经有大量的相关资料,下面几个链接都已经对Ziplist进行了详细的介绍. http://origin.r ...
【redis源码学习】simple dynamic strings（简单动态字符串 sds）
文章目录接化 sds 结构分析基本操作创建字符串释放字符串 sdsMakeRoomFor 扩容小tip:`__attribute__ ((__packed__))` 发接阅读源码之前, ...
redis源码解析（二）——SDS（简单动态字符串）
版本:redis - 5.0.4 参考资料:redis设计与实现文件:src下的sds.c sds.h 一.c语言中的字符串 vs SDS 二.sds.h 1.sdshdr header sds的存 ...
Redis笔记之基本数据结构动态字符串SDS
简单动态字符串传统上的C语言的字符串表示是以空字符结尾的字符数组(C字符串),redis自己实现一个动态字符串(SDS),两者之间的区别以及使用SDS的好处有: 结构不同.C字符串以空字符结尾的字符 ...

redis源码学习-03_动态字符串SDS

概述