最近在學習iniparser的原始碼，發現了C語言處理字串的大器（sscanf）！

具體的原始碼如下：
函式功能：解析一行字串，識別出 節名，鍵名，鍵值。

/*-------------------------------------------------------------------------*/
/**
  @brief    Load a single line from an INI file
  @param    input_line  Input line, may be concatenated multi-line input 可能存在拼接行
  @param    section     Output space to store section
  @param
 
    key         Output space to store key
  @param    value       Output space to store value
  @return   line_status value
 */
/*--------------------------------------------------------------------------*/
static line_status iniparser_line(
    const char * input_line,
    char * section,
    char * key,
    char
 
 * value)
{
    line_status sta ;
    char * line = NULL;
    size_t      len ;

    line = xstrdup(input_line);         //將入參存入臨時變數
    len = strstrip(line);               //刪除多於的空格

    sta = LINE_UNPROCESSED ;
    if (len<1) {
        /* Empty line  空行 */
        sta = LINE_EMPTY ;
    } else if (line[0
 
]=='#' || line[0]==';') {
        /* Comment line 註釋行 */
        sta = LINE_COMMENT ;
    } else if (line[0]=='[' && line[len-1]==']') {
        /* Section name  節名 */
        sscanf(line, "[%[^]]", section);    //跳過'[',取[]之間的字串內容
        strstrip(section);
        strlwc(section, section, len);      //轉換成小寫字元
        sta = LINE_SECTION ;
    } else if (sscanf (line, "%[^=] = \"%[^\"]\"", key, value) == 2    //等號左邊的值作為key,右邊作為value
           ||  sscanf (line, "%[^=] = '%[^\']'",   key, value) == 2) { // \' \" -- 表示轉義字元
        /* Usual key=value with quotes, with or without comments */    // 其中value帶引號
        strstrip(key);
        strlwc(key, key, len);
        /* Don't strip spaces from values surrounded with quotes  */
        sta = LINE_VALUE ;
    } else if (sscanf (line, "%[^=] = %[^;#]", key, value) == 2) {
        /* Usual key=value without quotes, with or without comments */
        strstrip(key);
        strlwc(key, key, len);
        strstrip(value);
        /*
         * sscanf cannot handle '' or "" as empty values
         * this is done here
         */
        if (!strcmp(value, "\"\"") || (!strcmp(value, "''"))) {
            value[0]=0 ;
        }
        sta = LINE_VALUE ;
    } else if (sscanf(line, "%[^=] = %[;#]", key, value)==2
           ||  sscanf(line, "%[^=] %[=]", key, value) == 2) {
        /*
         * Special cases:
         * key=
         * key=;
         * key=#
         */
        strstrip(key);
        strlwc(key, key, len);
        value[0]=0 ;
        sta = LINE_VALUE ;
    } else {
        /* Generate syntax error */
        sta = LINE_ERROR ;
    }

    free(line);
    return sta ;
}

下面咱們就來深度的剖析一下該神器，其中有用到了一些正則表示式的知識
這邊先列出一些基本的規則，我們之後一一驗證
1. %[^=] ； %[^A-Z] ； %[^;#] –取出特殊符號集（等號、A-Z、;#）之前的字串
2. [% ； a-c% ； @#% –過濾字串之前特殊符號集（[、 a-c、 @#）
3. %s ; %[0-9] ; –過濾字串之後特殊符號集（string、 0-9），該引數不需要儲存
4. %[0-9] ; –取出匹配特殊符號集的字串（0-9）

總結為， 左邊為需要過濾的內容 << % >> 右邊為需要取出的內容

測試程式碼如下：

/***************************************************** 
 * ** Name         : ini_sscanf.c  
 * ** Author       : lamar 
 * ** Version      : 1.0 
 * ** Date         : 2018-03 
 * ** Description  : test sscanf function 
 * ******************************************************/  
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

static void ini_sscanf(void)
{
    int     ret;
    char    *str;
    char    buf_1[1024];
    char    buf_2[1024];
    char    buf_3[1024];

    str = "Year=\"2018\"";
    ret = sscanf (str, "%[^=] = \"%[^\"]\"", buf_1, buf_2);
    printf("ret:%d, buf_1:%s buf_2:%s \n", ret, buf_1, buf_2);
    //執行結果：ret:2, buf_1:Year buf_2:2018 

    str = "abcYear=@#2018";
    ret = sscanf (str, "a%[^=]=%s", buf_1, buf_2);
    printf("ret:%d, buf_1:%s buf_2:%s \n", ret, buf_1, buf_2);
    //執行結果：ret:2, buf_1:bcYear buf_2:@#2018

    str = "abOcYear=@#2018";
    ret = sscanf (str, "%[a-z] %[^0-9]", buf_1, buf_3);
    printf("ret:%d, buf_1:%s buf_3:%s \n", ret, buf_1, buf_3);
    //執行結果：ret:2, buf_1:ab buf_3:OcYear=@#

    str = "abc=2018    year";
    ret = sscanf (str, "abc=%[0-9] %[^r]", buf_1, buf_2);
    printf("ret:%d, buf_1:%s buf_2:%s \n", ret, buf_1, buf_2);
    //執行結果：ret:2, buf_1:2018 buf_2:yea 

    str = "abc=2018 @@#lamar";
    ret = sscanf (str, "%*[^@] %[@#] %[a-z]", buf_1, buf_2);
    printf("ret:%d, buf_1:%s buf_2:%s \n", ret, buf_1, buf_2);
    //執行結果：ret:2, buf_1:@@# buf_2:lamar

    return ;
}

int main()
{
    ini_sscanf();

    printf("end the main function\n");

    return 0;
}

真乃為解析字串之大器！