redis源码剖析(十一)—— Redis字符串相关函数实现

文章目录

#define SDS_ABORT_ON_OOM

#include "sds.h"
#include stdio.h
#include stdlib.h
#include stdarg.h
#include string.h
#include ctype.h
#include "zmalloc.h"
//内存出错函数**封装的一个报错函数
static void sdsOomAbort(void) {
    //发生内存错误时向标准输出设备输出出错信息
    fprintf(stderr,"SDS: Out Of Memory (SDS_ABORT_ON_OOM defined)\n");
    abort();//出错时直接终止程序
}
初始化字符串
//新建一个字符串,并将其初始化,初始化时,取init字符串中initlen个字符
sds sdsnewlen(const void *init, size_t initlen) {
    struct sdshdr *sh;
    //创建字符串存储空间,多创建一个1,是因为C语言中的字符串
    //均有一个\0结束符
    sh = zmalloc(sizeof(struct sdshdr)+initlen+1);
#ifdef SDS_ABORT_ON_OOM
    //如果内存分配失败的情况下,直接终止程序的运行
    if (sh == NULL) sdsOomAbort();
#else
    //如果内存分配失败的情况下,返回NULL
    if (sh == NULL) return NULL;
#endif
    //记录内存空间的实际使用量
    sh-len = initlen;
    //记录内存空间的余下多少
    sh-free = 0;
    if (initlen) {
        //如果设置了init的情况下,复制initlen个字符
        if (init) memcpy(sh-buf, init, initlen);
        //否则将内存全部置为0
        else memset(sh-buf,0,initlen);
    }
    //结尾字符,C语言中字符串均以\0结尾
    sh-buf[initlen] = '\0';
    return (char*)sh-buf;
}

//生成一个空字符串,调用newlen()函数,开辟0个长度
sds sdsempty(void) {
    return sdsnewlen("",0);
}

/*
 * 生成一个新字符串
 * init表字生成新字符串时要拷贝进来的东西
 * 计算传进来的字符串长度,然后调用sdsnewlen()函数
 */
sds sdsnew(const char *init) {
    size_t initlen = (init == NULL) ? 0 : strlen(init);
    //传入 init的值,init的长度
    //返回的是
    //返回sdshdr这个结构体的return (char*)sh-buf;字符串长度
    return sdsnewlen(init, initlen);
}
字符串基本操作
/*
 * 获取字符串的长度
 * 字符串的长度是存放在sdshdr结构中的len里面
 */
size_t sdslen(const sds s) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    return sh-len;
}

/*
 * 对字符串进行复制
 */
sds sdsdup(const sds s) {
    return sdsnewlen(s, sdslen(s));
}

/*
 * 释放字符串
 */
void sdsfree(sds s) {
    if (s == NULL) return;
    zfree(s-sizeof(struct sdshdr));
}

/*
 * 返回字符串中还有多少空间可以使用
 */
size_t sdsavail(sds s) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    return sh-free;
}

/*
 * 更新字符串的长度
 */
void sdsupdatelen(sds s) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    int reallen = strlen(s);
    sh-free += (sh-len-reallen);
    sh-len = reallen;
}

/*
 * 给字符串增加长度
 */
static sds sdsMakeRoomFor(sds s, size_t addlen) {
    struct sdshdr *sh, *newsh;
    size_t free = sdsavail(s);
    size_t len, newlen;
    //如果余下空间还足够的话
    if (free = addlen) return s;
    len = sdslen(s);
    sh = (void*) (s-(sizeof(struct sdshdr)));
    newlen = (len+addlen)*2;
    newsh = zrealloc(sh, sizeof(struct sdshdr)+newlen+1);
    //内存分配失败的情况下进行处理
#ifdef SDS_ABORT_ON_OOM
    if (newsh == NULL) sdsOomAbort();
#else
    if (newsh == NULL) return NULL;
#endif
    //新的余下空间
    newsh-free = newlen - len;
    return newsh-buf;
}
字符串拼接操作
//进行字符串的拼接操作
sds sdscatlen(sds s, void *t, size_t len) {
    struct sdshdr *sh;
    size_t curlen = sdslen(s);

    s = sdsMakeRoomFor(s,len);
    if (s == NULL) return NULL;
    sh = (void*) (s-(sizeof(struct sdshdr)));
    memcpy(s+curlen, t, len);
    sh-len = curlen+len;
    sh-free = sh-free-len;
    s[curlen+len] = '\0';
    return s;
}

//同样进行字符串的拼接操作
sds sdscat(sds s, char *t) {
    return sdscatlen(s, t, strlen(t));
}

//进行字符串的copy,会覆盖掉原字符串
sds sdscpylen(sds s, char *t, size_t len) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    //字符串s代表的字符串的总共长度
    size_t totlen = sh-free+sh-len;

    if (totlen  len) {
        s = sdsMakeRoomFor(s,len-totlen);
        if (s == NULL) return NULL;
        sh = (void*) (s-(sizeof(struct sdshdr)));
        totlen = sh-free+sh-len;
    }
    memcpy(s, t, len);
    s[len] = '\0';
    sh-len = len;
    sh-free = totlen-len;
    return s;
}

//同样也是进行字符串的copy
//也会覆盖掉原字符串
sds sdscpy(sds s, char *t) {
    return sdscpylen(s, t, strlen(t));
}

//格式化拼接字符串
sds sdscatprintf(sds s, const char *fmt, ...) {
    va_list ap;
    char *buf, *t;
    size_t buflen = 32;

    while(1) {
        buf = zmalloc(buflen);
#ifdef SDS_ABORT_ON_OOM
        if (buf == NULL) sdsOomAbort();
#else
        if (buf == NULL) return NULL;
#endif
        buf[buflen-2] = '\0';
        //c语言中的可变参数的循环遍历
        va_start(ap, fmt);
        vsnprintf(buf, buflen, fmt, ap);
        va_end(ap);
        if (buf[buflen-2] != '\0') {
            zfree(buf);
            buflen *= 2;
            continue;
        }
        break;
    }
    //对字符串进行拼接
    t = sdscat(s, buf);
    zfree(buf);
    return t;
}
other
//字符串中去掉首尾包含cset里的字符
sds sdstrim(sds s, const char *cset) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    char *start, *end, *sp, *ep;
    size_t len;
    //字符串的开始位置
    sp = start = s;
    //字符串的结束位置
    ep = end = s+sdslen(s)-1;
    //查看字符串cset中首次出现字符*sp的位置
    while(sp = end  strchr(cset, *sp)) sp++;
    //查找字符串cset中首次出现字符*ep的位置
    while(ep  start  strchr(cset, *ep)) ep--;
    len = (sp  ep) ? 0 : ((ep-sp)+1);
    //字符串的内存移动操作
    if (sh-buf != sp) memmove(sh-buf, sp, len);
    sh-buf[len] = '\0';
    //字符串的余下空间增长
    sh-free = sh-free+(sh-len-len);
    sh-len = len;
    return s;
}
获取指定范围里的字符串
sds sdsrange(sds s, long start, long end) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    size_t newlen, len = sdslen(s);

    if (len == 0) return s;
    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) start = len-1;
        if (end = (signed)len) end = len-1;
        newlen = (start  end) ? 0 : (end-start)+1;
    } else {
        start = 0;
    }
    if (start != 0) memmove(sh-buf, sh-buf+start, newlen);
    sh-buf[newlen] = 0;
    sh-free = sh-free+(sh-len-newlen);
    sh-len = newlen;
    return s;
}
将字符串中的所有字符均转为小写的形式
void sdstolower(sds s) {
    int len = sdslen(s), j;
    for (j = 0; j  len; j++) s[j] = tolower(s[j]);
}
将字符串中所有字符均转为大写的形式
void sdstoupper(sds s) {
    int len = sdslen(s), j;
    for (j = 0; j  len; j++) s[j] = toupper(s[j]);
}
字符串比较
//对两个字符串进行比较
int sdscmp(sds s1, sds s2) {
    size_t l1, l2, minlen;
    int cmp;
    l1 = sdslen(s1);
    l2 = sdslen(s2);
    minlen = (l1  l2) ? l1 : l2;//返回短的
    cmp = memcmp(s1,s2,minlen);//该函数返回一个指向目标存储区s1的指针。
    if (cmp == 0) return l1-l2;//两者不相等,cmp=0
    return cmp;
}

other
/* 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 *sdssplitlen(char *s, int len, char *sep, int seplen, int *count) {
    int elements = 0, slots = 5, start = 0, j;
    //开设5字节的内存空间
    //实际开设时会开设6字节,具体可以参看zmallo.c里的源代码
    sds *tokens = zmalloc(sizeof(sds)*slots);
#ifdef SDS_ABORT_ON_OOM
    if (tokens == NULL) sdsOomAbort();
#endif
    if (seplen  1 || len  0 || tokens == NULL) return NULL;
    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) {
#ifdef SDS_ABORT_ON_OOM
                sdsOomAbort();
#else
                goto cleanup;
#endif
            }
            tokens = newtokens;
        }
        /* search the separator */
        if ((seplen == 1  *(s+j) == sep[0]) || (memcmp(s+j,sep,seplen) == 0)) {
            //计算分割符以前的字符串的长度
            tokens[elements] = sdsnewlen(s+start,j-start);
            if (tokens[elements] == NULL) {
#ifdef SDS_ABORT_ON_OOM
                sdsOomAbort();//失败的情况下,如果定义了内存失败函数,将直接调用
#else
                goto cleanup;//否则跳到cleanup函数,进行一个一个的释放
#endif
            }
            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. */
    //分割串里面的最后一个字符串
    tokens[elements] = sdsnewlen(s+start,len-start);
    if (tokens[elements] == NULL) {
#ifdef SDS_ABORT_ON_OOM
                sdsOomAbort();
#else
                goto cleanup;
#endif
    }
    elements++;
    //传的是个引用,可以获取最终分割为多少个数组
    *count = elements;
    return tokens;

#ifndef SDS_ABORT_ON_OOM
//如果没有定义分配失败的情况下,内存操作函数
//将会一个一个的调用内存失败处理函数
cleanup:
    {
        int i;
        for (i = 0; i  elements; i++) sdsfree(tokens[i]);
        zfree(tokens);
        return NULL;
    }
#endif
}
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