（四）sds字符串

[cpp] 
/* 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 
 
/* 最大分配内存1M */ 
#define SDS_MAX_PREALLOC (1024*1024) 
 
#include <sys/types.h> 
#include <stdarg.h> 
 
/* 声明了sds的一种char类型 */ 
typedef char *sds;  
 
/* 字符串结构体类型 */ 
struct sdshdr {  
 //字符长度 
    unsigned int len;  
 //当前可用空间 
    unsigned int free;  
 //具体存放字符的buf 
 char buf[];  
};  
 
/* 计算sds的长度，返回的size_t类型的数值 */ 
/* size_t,它是一个与机器相关的unsigned类型，其大小足以保证存储内存中对象的大小。 */ 
static inline size_t sdslen(const sds s) {  
 struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));  
 return sh->len;  
}  
 
/* 根据sdshdr中的free标记获取可用空间 */ 
static inline size_t sdsavail(const sds s) {  
 struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));  
 return sh->free;  
}  
 
sds sdsnewlen(const void *init, size_t initlen);   //根据给定长度，新生出一个sds 
sds sdsnew(const char *init);    //根据给定的值，生出sds 
sds sdsempty(void);    //清空sds操作 
size_t sdslen(const sds s);   //获取sds的长度 
sds sdsdup(const sds s);   //sds的复制方法 
void sdsfree(sds s);   //sds的free释放方法 
size_t sdsavail(const sds s);   //判断sds获取可用空间 
sds sdsgrowzero(sds s, size_t len); // 扩展字符串到指定的长度  
sds sdscatlen(sds s, const void *t, size_t len);  
sds sdscat(sds s, const char *t);    //sds连接上char字符 
sds sdscatsds(sds s, const sds t);  //sds连接上sds 
sds sdscpylen(sds s, const char *t, size_t len);  //字符串复制相关 
sds sdscpy(sds s, const char *t); //字符串复制相关 
 
sds sdscatvprintf(sds s, const char *fmt, va_list ap);   //字符串格式化输出，依赖已有的方法sprintf，效率不及下面自己写的 
#ifdef __GNUC__ 
sds sdscatprintf(sds s, const char *fmt, ...)  
    __attribute__((format(printf, 2, 3)));  
#else 
sds sdscatprintf(sds s, const char *fmt, ...);  
#endif 
 
sds sdscatfmt(sds s, char const *fmt, ...);   //字符串格式化输出 
sds sdstrim(sds s, const char *cset);       //字符串缩减 
void sdsrange(sds s, int start, int end);   //字符串截取函数 
void sdsupdatelen(sds s);   //更新字符串最新的长度 
void sdsclear(sds s);   //字符串清空操作 
int sdscmp(const sds s1, const sds s2);   //sds比较函数 
sds *sdssplitlen(const char *s, int len, const char *sep, int seplen, int *count);  //字符串分割子字符串 
void sdsfreesplitres(sds *tokens, int count);  //释放子字符串数组 
void sdstolower(sds s);    //sds字符转小写表示 
void sdstoupper(sds s);    //sds字符统一转大写 
sds sdsfromlonglong(long long value);   //生出数组字符串 
sds sdscatrepr(sds s, const char *p, size_t len);  
sds *sdssplitargs(const char *line, int *argc);   //参数拆分 
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen); //字符映射,"ho", "01", h映射为0， o映射为1 
sds sdsjoin(char **argv, int argc, char *sep);   //以分隔符连接字符串子数组构成新的字符串 
 
/* Low level functions exposed to the user API */ 
/* 开放给使用者的API */ 
sds sdsMakeRoomFor(sds s, size_t addlen);  
void sdsIncrLen(sds s, int incr);  
sds sdsRemoveFreeSpace(sds s);  
size_t sdsAllocSize(sds s);  
 
#endif 

[cpp]
/* 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. */ 
/* 清空字符串 */ 
void sdsclear(sds s) {  
 struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));  
 //空闲的长度增多 
    sh->free += sh->len;  
    sh->len = 0;  
 //字符串中的缓存其实没有被丢底，只是把第一个设成了结束标志，以便下次操作可以复用 
    sh->buf[0] = '\0';  
}  

[cpp]
/* 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. */ 
/* 创建新字符串方法，传入目标长度，初始化方法 */ 
sds sdsnewlen(const void *init, size_t initlen) {  
 struct sdshdr *sh;  
 
 if (init) {  
        sh = zmalloc(sizeof(struct sdshdr)+initlen+1);  
    } else {  
 //当init函数为NULL时候，又来了zcalloc的方法 
        sh = zcalloc(sizeof(struct sdshdr)+initlen+1);  
    }  
 if (sh == NULL) return NULL;  
    sh->len = initlen;  
    sh->free = 0;  
 if (initlen && init)  
        memcpy(sh->buf, init, initlen);  
 //最末端同样要加‘\0’结束符 
    sh->buf[initlen] = '\0';  
 //最后是通过返回字符串结构体中的buf代表新的字符串 
 return (char*)sh->buf;  
}  

[cpp] 
/* 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. 
 */ 
/* 字符串格式化输出，输入原字符串，格式，参数 */ 
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. */ 
 //关键再次，以此比较输入的格式类型 
 while(*f) {  
 char next, *str;  
        unsigned int 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 '%':  
 /*如果是%,记住百分号后面的类型操作值*/ 
            next = *(f+1);  
            f++;  
 switch(next) {  
 case 's':  
 case 'S':  
                str = va_arg(ap,char*);  
 //判断普通的str,还是sds类型，计算长度的方法不一样 
                l = (next == 's') ? strlen(str) : sdslen(str);  
 if (sh->free < l) {  
                    s = sdsMakeRoomFor(s,l);  
                    sh = (void*) (s-(sizeof(struct sdshdr)));  
                }  
 //如果是字符串，直接复制到后面 
                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);  
 else 
                    num = va_arg(ap,long long);  
                {  
 char buf[SDS_LLSTR_SIZE];  
 //如果是数字，调用添加数值字符串方法 
                    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':  
 //无符号整型同上 
 if (next == 'u')  
                    unum = va_arg(ap,unsigned int);  
 else 
                    unum = 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:  
 //非操作类型，直接单字符添加 
            s[i++] = *f;  
            sh->len += 1;  
            sh->free -= 1;  
 break;  
        }  
        f++;  
    }  
    va_end(ap);  
 
 /* Add null-term */ 
    s[i] = '\0';  
 return s;  
}  

看完的确让我感觉很强大，小小的格式化输出，竟然也没有那么简单，应该java，里的格式化输出算法应该都是跟这差不多的吧。另外一个拆分split方法，这个里面竟然还因为内存的问题的用了goto清空间操作，这个也是涨见识了：

[cpp] 
/* 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. 
 * 
 * On out of memory, zero length string, zero length 
 * separator, NULL is returned. 
 * 
 * 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". 
 * 
 * This version of the function is binary-safe but 
 * requires length arguments. sdssplit() is just the 
 * same function but for zero-terminated strings. 
 */ 
/* sds字符串分割方法类似java.lang.String的spilt方法 */ 
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;  
 
 //分割的子字符串初始值只有5组 
    tokens = zmalloc(sizeof(sds)*slots);  
 //如果内存溢出，直接返回NULL值 
 if (tokens == NULL) return NULL;  
 
 if (len == 0) {  
        *count = 0;  
 return tokens;  
    }  
 //从前往后扫描，到最后一个能匹配分隔符字符串的位置len-seplen 
 for (j = 0; j < (len-(seplen-1)); j++) {  
 /* make sure there is room for the next element and the final one */ 
 //如果当前字符串数组数量少于当前已存在数组+2个的时候，动态添加 
 if (slots < elements+2) {  
            sds *newtokens;  
 
            slots *= 2;  
            newtokens = zrealloc(tokens,sizeof(sds)*slots);  
 //如果内存此时溢出，goto语句free释放内存，终于看到了goto语句的派上用处了 
 if (newtokens == NULL) goto cleanup;  
            tokens = newtokens;  
        }  
 /* search the separator */ 
 //分成单字符比较和多字符比较匹配 
 if ((seplen == 1 && *(s+j) == sep[0]) || (memcmp(s+j,sep,seplen) == 0)) {  
 //赋值子字符串 
            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. */ 
 //最后一个字符串添加 
    tokens[elements] = sdsnewlen(s+start,len-start);  
 //如果内存溢出，再次清空，也直接直接返回NULL 
 if (tokens[elements] == NULL) goto cleanup;  
    elements++;  
    *count = elements;  
 return tokens;  
 
cleanup:  
    {  
 //清除空间 
 int i;  
 for (i = 0; i < elements; i++) sdsfree(tokens[i]);  
        zfree(tokens);  
        *count = 0;  
 return NULL;  
    }  
}  

[cpp]
/* 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'. */ 
/* 字符串末尾添加数值字符串组成新的字符串 */ 
#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;  
 //用最传统的逐位取商算出每一个位置上的数，注意现在的顺序其实是逆序的 
 do {  
        *p++ = '0'+(v%10);  
        v /= 10;  
    } while(v);  
 //后面别忘了正负号的添加 
 if (value < 0) *p++ = '-';  
 
 /* Compute length and add null term. */ 
    l = p-s;  
    *p = '\0';  
 
 /* Reverse the string. */ 
 //将刚才的添加的逆序的数字字符串进行倒叙添加到本身的字符串s中 
    p--;  
 while(s < p) {  
        aux = *s;  
        *s = *p;  
        *p = aux;  
        s++;  
        p--;  
    }  
 return l;  
}  

[cpp] 
/* 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. 
 * 
 * For instance: sdsmapchars(mystring, "ho", "01", 2) 
 * will have the effect of turning the string "hello" into "0ell1". 
 * 
 * The function returns the sds string pointer, that is always the same 
 * as the input pointer since no resize is needed. */ 
/* 字符映射,"ho", "01", h映射为0， o映射为1 */ 
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {  
 size_t j, i, l = sdslen(s);  
 
 for (j = 0; j < l; j++) {  
 for (i = 0; i < setlen; i++) {  
 if (s[j] == from[i]) {  
                s[j] = to[i];  
 break;  
            }  
        }  
    }  
 return s;  
}