公司做一个网站如何定位,如何用vps做网站,模板图片 背景,ol游戏大全排行榜cJSON数据解析 关于数据解析部分#xff0c;其实这个解析就是个自动机#xff0c;通过递归或者解析栈进行实现数据的解析 /* Utility to jump whitespace and cr/lf *///用于跳过ascii小于32的空白字符
static const char *skip(const char *in)
{ while (in *in…cJSON数据解析 关于数据解析部分其实这个解析就是个自动机通过递归或者解析栈进行实现数据的解析 /* Utility to jump whitespace and cr/lf *///用于跳过ascii小于32的空白字符
static const char *skip(const char *in)
{ while (in *in (unsigned char)*in 32)in;return in;
}/* Parse an object - create a new root, and populate. */
cJSON *cJSON_ParseWithOpts(const char *value, const char **return_parse_end, int require_null_terminated)
{const char *end 0;cJSON *c cJSON_New_Item();ep 0;if (!c) return 0; /* memory fail *///根据前几个字符设置c类型并更新读取位置为endend parse_value(c, skip(value));if (!end){ cJSON_Delete(c); //解析失败数据不完整return 0; } /* parse failure. ep is set. *//* if we require null-terminated JSON without appended garbage, skip and then check for a null terminator */if (require_null_terminated)///??{ end skip(end); if (*end){ cJSON_Delete(c); ep end; return 0;}}if (return_parse_end)*return_parse_end end;return c;
}
/* Default options for cJSON_Parse */
cJSON *cJSON_Parse(const char *value) { return cJSON_ParseWithOpts(value, 0, 0); } ①关于重点部分parse_value 对类型解读函数 /* Parser core - when encountering text, process appropriately. *///将输入字符串解析为具体类型cJSON结构
static const char *parse_value(cJSON *item, const char *value)
{if (!value) return 0; /* Fail on null. */ //设置结构的具体类型并且返回下一个将要解读数据的位置if (!strncmp(value, null, 4)) { item-type cJSON_NULL; return value 4; }if (!strncmp(value, false, 5)) { item-type cJSON_False; return value 5; }if (!strncmp(value, true, 4)) { item-type cJSON_True; item-valueint 1; return value 4; }if (*value \) { return parse_string(item, value); }if (*value - || (*value 0 *value 9)) { return parse_number(item, value); }if (*value [) { return parse_array(item, value); }if (*value {) { return parse_object(item, value); }ep value; return 0; /* failure. */
} ②解析字符串部分解析字符串时 对于特殊字符也应该转义比如 n 字符应该转换为 n 这个换行符。当然如果只有特殊字符转换的话代码不会又这么长 对于字符串 还要支持非 ascii 码的字符 即 utf8字符。这些字符在字符串中会编码为 uXXXX 的字符串 我们现在需要还原为 0 - 255 的一个字符。 static unsigned parse_hex4(const char *str)
{unsigned h 0;if (*str 0 *str 9) h (*str) - 0;else if (*str A *str F)h 10 (*str) - A;else if (*str a *str f)h 10 (*str) - a; else return 0;h h 4; //*Fstr;if (*str 0 *str 9)h (*str) - 0; else if (*str A *str F)h 10 (*str) - A; else if (*str a *str f) h 10 (*str) - a; elsereturn 0;h h 4;str;if (*str 0 *str 9)h (*str) - 0; else if (*str A *str F)h 10 (*str) - A;else if (*str a *str f)h 10 (*str) - a;else return 0;h h 4; str;if (*str 0 *str 9)h (*str) - 0; else if (*str A *str F)h 10 (*str) - A;else if (*str a *str f)h 10 (*str) - a; else return 0;return h;
}/* Parse the input text into an unescaped cstring, and populate item. */
static const unsigned char firstByteMark[7] { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };
static const char *parse_string(cJSON *item, const char *str)
{const char *ptr str 1;char *ptr2; char *out;int len 0; unsigned uc, uc2;if (*str ! \) { ep str; return 0; } /* not a string! */while(*ptr ! \ *ptr len)if (*ptr \\) //跳过\续行符ptr; /* Skip escaped quotes. *///空间申请out (char*)cJSON_malloc(len 1); /* This is how long we need for the string, roughly. */if (!out) return 0;ptr str 1;//跳过“开始ptr2 out;while (*ptr ! \ *ptr){if (*ptr ! \\)*ptr2 *ptr;else //转义字符处理{ptr;switch (*ptr){case b: *ptr2 \b; break;case f: *ptr2 \f; break;case n: *ptr2 \n; break;case r: *ptr2 \r; break;case t: *ptr2 \t; break;case u: /* transcode utf16 to utf8. */uc parse_hex4(ptr 1); ptr 4; /* get the unicode char. */if ((uc 0xDC00 uc 0xDFFF) || uc 0) break; /* check for invalid. */if (uc 0xD800 uc 0xDBFF) /* UTF16 surrogate pairs. */{if (ptr[1] ! \\ || ptr[2] ! u) break; /* missing second-half of surrogate. */uc2 parse_hex4(ptr 3);ptr 6;if (uc20xDC00 || uc20xDFFF) break; /* invalid second-half of surrogate. */uc 0x10000 (((uc 0x3FF) 10) | (uc2 0x3FF));}len 4; if (uc0x80)len 1;else if (uc0x800)len 2; else if (uc0x10000) len 3;ptr2 len;switch (len){case 4:*--ptr2 ((uc | 0x80) 0xBF); uc 6;case 3:*--ptr2 ((uc | 0x80) 0xBF); uc 6;case 2:*--ptr2 ((uc | 0x80) 0xBF); uc 6;case 1:*--ptr2 (uc | firstByteMark[len]);}ptr2 len;break;default:*ptr2 *ptr; break;}ptr;}}*ptr2 0;if (*ptr \) ptr;item-valuestring out;item-type cJSON_String;return ptr;
} 关于具体的字符解析中的编码相关问题请自行阅读编码相关知识 ③数字解析 /* Parse the input text to generate a number, and populate the result into item. */
static const char *parse_number(cJSON *item, const char *num)
{double n 0, sign 1, scale 0; int subscale 0,signsubscale 1;if (*num -)sign -1, num; /* Has sign? */if (*num 0) num; /* is zero */if (*num 1 *num 9) do {n (n*10.0) (*num - 0);}while (*num 0 *num 9); /* Number? */if (*num . num[1] 0 num[1] 9){ num; don (n*10.0) (*num - 0), scale--;while (*num 0 *num 9); } /* Fractional part? */if (*num e || *num E) /* Exponent? */{num;if (*num )num; else if (*num -)signsubscale -1, num; /* With sign? */while (*num 0 *num 9)subscale (subscale * 10) (*num - 0); /* Number? */}n sign*n*pow(10.0, (scale subscale*signsubscale)); /* number /- number.fraction * 10^/- exponent */item-valuedouble n;item-valueint (int)n;item-type cJSON_Number;return num;
} ④解析数组解析数组 需要先遇到 [ 这个符号 然后挨个的读取节点内容 节点使用 , 分隔 , 前后还可能有空格 最后以 ] 结尾。我们要编写的也是这样。先创建一个数组对象 判断是否有儿子 有的话读取第一个儿子 然后判断是不是有 逗号 有的话循环读取后面的儿子。最后读取 ] 即可。 /* Build an array from input text. */
static const char *parse_array(cJSON *item, const char *value)
{cJSON *child;if (*value ! [) {ep value;return 0;} /* not an array! */item-type cJSON_Array;value skip(value 1);if (*value ])return value 1; /* empty array. */item-child child cJSON_New_Item();if (!item-child) return 0; /* memory fail *///解析数组内结构value skip(parse_value(child, skip(value))); /* skip any spacing, get the value. */if (!value) return 0;while (*value ,){cJSON *new_item;if (!(new_item cJSON_New_Item())) return 0; /* memory fail */child-next new_item; new_item-prev child;child new_item;value skip(parse_value(child, skip(value 1)));if (!value)return 0; /* memory fail */}if (*value ])return value 1; /* end of array */ep value; return 0; /* malformed. */
} ⑤解析对象 解析对象和解析数组类似 只不过对象的一个儿子是个 key - value, key 是字符串 value 可能是任何值 key 和 value 用 : 分隔。 /* Render an object to text. */
static char *print_object(cJSON *item, int depth, int fmt, printbuffer *p)
{char **entries 0, **names 0;char *out 0, *ptr, *ret, *str; int len 7, i 0, j;cJSON *child item-child;int numentries 0, fail 0;size_t tmplen 0;/* Count the number of entries. */while (child) numentries, child child-next;/* Explicitly handle empty object case */if (!numentries){if (p) out ensure(p, fmt ? depth 4 : 3);else out (char*)cJSON_malloc(fmt ? depth 4 : 3);if (!out) return 0;ptr out; *ptr {;if (fmt) { *ptr \n; for (i 0; idepth - 1; i) *ptr \t; }*ptr }; *ptr 0;return out;}if (p){/* Compose the output: */i p-offset;len fmt ? 2 : 1; ptr ensure(p, len 1); if (!ptr) return 0;*ptr {; if (fmt) *ptr \n; *ptr 0; p-offset len;child item-child; depth;while (child){if (fmt){ptr ensure(p, depth); if (!ptr) return 0;for (j 0; jdepth; j) *ptr \t;p-offset depth;}print_string_ptr(child-string, p);p-offset update(p);len fmt ? 2 : 1;ptr ensure(p, len); if (!ptr) return 0;*ptr :; if (fmt) *ptr \t;p-offset len;print_value(child, depth, fmt, p);p-offset update(p);len (fmt ? 1 : 0) (child-next ? 1 : 0);ptr ensure(p, len 1); if (!ptr) return 0;if (child-next) *ptr ,;if (fmt) *ptr \n; *ptr 0;p-offset len;child child-next;}ptr ensure(p, fmt ? (depth 1) : 2); if (!ptr) return 0;if (fmt) for (i 0; idepth - 1; i) *ptr \t;*ptr }; *ptr 0;out (p-buffer) i;}else{/* Allocate space for the names and the objects */entries (char**)cJSON_malloc(numentries * sizeof(char*));if (!entries) return 0;names (char**)cJSON_malloc(numentries * sizeof(char*));if (!names) { cJSON_free(entries); return 0; }memset(entries, 0, sizeof(char*)*numentries);memset(names, 0, sizeof(char*)*numentries);/* Collect all the results into our arrays: */child item-child; depth; if (fmt) len depth;while (child){names[i] str print_string_ptr(child-string, 0);entries[i] ret print_value(child, depth, fmt, 0);if (str ret) len strlen(ret) strlen(str) 2 (fmt ? 2 depth : 0); else fail 1;child child-next;}/* Try to allocate the output string */if (!fail) out (char*)cJSON_malloc(len);if (!out) fail 1;/* Handle failure */if (fail){for (i 0; inumentries; i) { if (names[i]) cJSON_free(names[i]); if (entries[i]) cJSON_free(entries[i]); }cJSON_free(names); cJSON_free(entries);return 0;}/* Compose the output: */*out {; ptr out 1; if (fmt)*ptr \n; *ptr 0;for (i 0; inumentries; i){if (fmt) for (j 0; jdepth; j) *ptr \t;tmplen strlen(names[i]); memcpy(ptr, names[i], tmplen); ptr tmplen;*ptr :; if (fmt) *ptr \t;strcpy(ptr, entries[i]); ptr strlen(entries[i]);if (i ! numentries - 1) *ptr ,;if (fmt) *ptr \n; *ptr 0;cJSON_free(names[i]); cJSON_free(entries[i]);}cJSON_free(names); cJSON_free(entries);if (fmt) for (i 0; idepth - 1; i) *ptr \t;*ptr }; *ptr 0;}return out;
} 这样都实现后 字符串解析为 json 对象就实现了。 ⑥序列化 序列化也就是格式化输出了。 序列化又分为格式化输出压缩输出 /* Render a cJSON item/entity/structure to text. */
char *cJSON_Print(cJSON *item)
{ return print_value(item, 0, 1, 0);
}
char *cJSON_PrintUnformatted(cJSON *item)
{return print_value(item, 0, 0, 0);
}char *cJSON_PrintBuffered(cJSON *item, int prebuffer, int fmt)
{printbuffer p;p.buffer (char*)cJSON_malloc(prebuffer);p.length prebuffer;p.offset 0;return print_value(item, 0, fmt, p);return p.buffer;
}/* Render a value to text. */
static char *print_value(cJSON *item, int depth, int fmt, printbuffer *p)
{char *out 0;if (!item) return 0;if (p){switch ((item-type) 255){case cJSON_NULL: {out ensure(p, 5); if (out) strcpy(out, null); break; }case cJSON_False: {out ensure(p, 6); if (out) strcpy(out, false); break; }case cJSON_True: {out ensure(p, 5); if (out) strcpy(out, true); break; }case cJSON_Number: out print_number(item, p); break;case cJSON_String: out print_string(item, p); break;case cJSON_Array: out print_array(item, depth, fmt, p); break;case cJSON_Object: out print_object(item, depth, fmt, p); break;}}else{switch ((item-type) 255){case cJSON_NULL: out cJSON_strdup(null); break;case cJSON_False: out cJSON_strdup(false); break;case cJSON_True: out cJSON_strdup(true); break;case cJSON_Number: out print_number(item, 0); break;case cJSON_String: out print_string(item, 0); break;case cJSON_Array: out print_array(item, depth, fmt, 0); break;case cJSON_Object: out print_object(item, depth, fmt, 0); break;}}return out;
} 假设我们要使用格式化输出 也就是美化输出。 cjson 的做法不是边分析 json 边输出 而是预先将要输的内容全部按字符串存在内存中 最后输出整个字符串。 这对于比较大的 json 来说 内存就是个问题了。 另外格式化输出依靠的是节点的深度 这个也可以优化 一般宽度超过80 时 就需要从新的一行算起的。 /* Render an object to text. */
static char *print_object(cJSON *item, int depth, int fmt, printbuffer *p)
{char **entries 0, **names 0;char *out 0, *ptr, *ret, *str; int len 7, i 0, j;cJSON *child item-child;int numentries 0, fail 0;size_t tmplen 0;/* Count the number of entries. */while (child) numentries, child child-next;/* Explicitly handle empty object case */if (!numentries){if (p) out ensure(p, fmt ? depth 4 : 3);else out (char*)cJSON_malloc(fmt ? depth 4 : 3);if (!out) return 0;ptr out; *ptr {;if (fmt) { *ptr \n; for (i 0; idepth - 1; i) *ptr \t; }*ptr }; *ptr 0;return out;}if (p){/* Compose the output: */i p-offset;len fmt ? 2 : 1; ptr ensure(p, len 1); if (!ptr) return 0;*ptr {; if (fmt) *ptr \n; *ptr 0; p-offset len;child item-child; depth;while (child){if (fmt){ptr ensure(p, depth); if (!ptr) return 0;for (j 0; jdepth; j) *ptr \t;p-offset depth;}print_string_ptr(child-string, p);p-offset update(p);len fmt ? 2 : 1;ptr ensure(p, len); if (!ptr) return 0;*ptr :; if (fmt) *ptr \t;p-offset len;print_value(child, depth, fmt, p);p-offset update(p);len (fmt ? 1 : 0) (child-next ? 1 : 0);ptr ensure(p, len 1); if (!ptr) return 0;if (child-next) *ptr ,;if (fmt) *ptr \n; *ptr 0;p-offset len;child child-next;}ptr ensure(p, fmt ? (depth 1) : 2); if (!ptr) return 0;if (fmt) for (i 0; idepth - 1; i) *ptr \t;*ptr }; *ptr 0;out (p-buffer) i;}else{/* Allocate space for the names and the objects */entries (char**)cJSON_malloc(numentries * sizeof(char*));if (!entries) return 0;names (char**)cJSON_malloc(numentries * sizeof(char*));if (!names) { cJSON_free(entries); return 0; }memset(entries, 0, sizeof(char*)*numentries);memset(names, 0, sizeof(char*)*numentries);/* Collect all the results into our arrays: */child item-child; depth; if (fmt) len depth;while (child){names[i] str print_string_ptr(child-string, 0);entries[i] ret print_value(child, depth, fmt, 0);if (str ret) len strlen(ret) strlen(str) 2 (fmt ? 2 depth : 0); else fail 1;child child-next;}/* Try to allocate the output string */if (!fail) out (char*)cJSON_malloc(len);if (!out) fail 1;/* Handle failure */if (fail){for (i 0; inumentries; i) { if (names[i]) cJSON_free(names[i]); if (entries[i]) cJSON_free(entries[i]); }cJSON_free(names); cJSON_free(entries);return 0;}/* Compose the output: */*out {; ptr out 1; if (fmt)*ptr \n; *ptr 0;for (i 0; inumentries; i){if (fmt) for (j 0; jdepth; j) *ptr \t;tmplen strlen(names[i]); memcpy(ptr, names[i], tmplen); ptr tmplen;*ptr :; if (fmt) *ptr \t;strcpy(ptr, entries[i]); ptr strlen(entries[i]);if (i ! numentries - 1) *ptr ,;if (fmt) *ptr \n; *ptr 0;cJSON_free(names[i]); cJSON_free(entries[i]);}cJSON_free(names); cJSON_free(entries);if (fmt) for (i 0; idepth - 1; i) *ptr \t;*ptr }; *ptr 0;}return out;
} static char *print_array(cJSON *item, int depth, int fmt, printbuffer *p)
{char **entries;char *out 0, *ptr, *ret; int len 5;cJSON *child item-child;int numentries 0, i 0, fail 0;size_t tmplen 0;/* How many entries in the array? */while (child) numentries, child child-next;/* Explicitly handle numentries0 */if (!numentries){if (p) out ensure(p, 3);else out (char*)cJSON_malloc(3);if (out) strcpy(out, []);return out;}if (p){/* Compose the output array. */i p-offset;ptr ensure(p, 1); if (!ptr) return 0; *ptr [; p-offset;child item-child;while (child !fail){print_value(child, depth 1, fmt, p);p-offset update(p);if (child-next) { len fmt ? 2 : 1; ptr ensure(p, len 1); if (!ptr) return 0; *ptr ,; if (fmt)*ptr ; *ptr 0; p-offset len; }child child-next;}ptr ensure(p, 2); if (!ptr) return 0; *ptr ]; *ptr 0;out (p-buffer) i;}else{/* Allocate an array to hold the values for each */entries (char**)cJSON_malloc(numentries * sizeof(char*));if (!entries) return 0;memset(entries, 0, numentries * sizeof(char*));/* Retrieve all the results: */child item-child;while (child !fail){ret print_value(child, depth 1, fmt, 0);entries[i] ret;if (ret) len strlen(ret) 2 (fmt ? 1 : 0); else fail 1;child child-next;}/* If we didnt fail, try to malloc the output string */if (!fail) out (char*)cJSON_malloc(len);/* If that fails, we fail. */if (!out) fail 1;/* Handle failure. */if (fail){for (i 0; inumentries; i) if (entries[i]) cJSON_free(entries[i]);cJSON_free(entries);return 0;}/* Compose the output array. */*out [;ptr out 1; *ptr 0;for (i 0; inumentries; i){tmplen strlen(entries[i]); memcpy(ptr, entries[i], tmplen); ptr tmplen;if (i ! numentries - 1) { *ptr ,; if (fmt)*ptr ; *ptr 0; }cJSON_free(entries[i]);}cJSON_free(entries);*ptr ]; *ptr 0;}return out;
} 转载于:https://www.cnblogs.com/lang5230/p/5492702.html
