atoX 与 strtoX

在很多时候我们都很清楚 atoX 系列函数: atoi , atol , atof
新来的一系列函数:  strtol,  strtoul, strtod 
通常有如下的关系：
1. 对应关系其中： 

          atoi   (把字符串转到整形)    --对应--   strtol  (把字符串转到长整形)           

          atol   (把字符串转到长整形)    --对应--   strtol  (把字符串转到长整形)           

          atof   (把字符串转到浮点数)    --对应--   strtod (把字符串转到浮点数) 
2. atoX 系列是 三十年前的函数 strtoX 系列是后十年产品

3. atoX 系列接口，没有成功失败的区别(标准实现中)，    strtoX 系列接口，有成功失败的区别

    比如：int i_atoi_lfs =  atoi(""); 与 int i_atoi_rfs = atoi("0"); 两个得到的是一样的，没有任何区别         

     而： int i_atoi_lfs =  strtol  ("", NULL,10); 与 int i_atoi_rfs = strtol  ("0", NULL,10);  得到的结果都是0，但是左边会置失败标志位。

4. msvcr80.dll  的具体实现：

 

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int __cdecl atoi(__in_zconst char *_Str){  return_tstoi(_Str);  }   

int __cdecl _tstoi(     const _TCHAR *nptr        ){    return (int)_tstol(nptr);}

int __cdecl _tstoi(     const _TCHAR *nptr        ){    return (int)_tstol(nptr);}

long __cdecl _tstol(const _TCHAR *nptr){return _tcstol(nptr, NULL, 10);}

#define _tcstol   strtol

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<pre class="brush:cpp">extern"C" long __cdecl strtol (

        constchar *nptr,

        char**endptr,

        intibase

        )

{

    if(__locale_changed == 0)

    {

        return(long) strtoxl(&__initiallocalestructinfo, nptr, (constchar **)endptr, ibase, 0);

    }

    else

    {

        return(long) strtoxl(NULL, nptr, (constchar **)endptr, ibase, 0);

    }

}

</pre>

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staticunsigned long__cdecl strtoxl (

        _locale_t plocinfo,

        constchar *nptr,

        constchar **endptr,

        intibase,

        intflags

        )

{

        constchar *p;

        charc;

        unsignedlong number;

        unsigned digval;

        unsignedlong maxval;

        _LocaleUpdate _loc_update(plocinfo);

 

        /* validation section */

        if(endptr != NULL)

        {

            /* store beginning of string in endptr */

            *endptr = (char*)nptr;

        }

        _VALIDATE_RETURN(nptr != NULL, EINVAL, 0L);

        _VALIDATE_RETURN(ibase == 0 || (2 <= ibase && ibase <= 36), EINVAL, 0L);

 

        p = nptr;                      /* p is our scanning pointer */

        number = 0;                    /* start with zero */

//1. 这里关注到，函数没有检查传入的原字符指针是否为空, 如果传递了一个空的就崩了....

        c = *p++;                      /* read char */

        while( _isspace_l((int)(unsignedchar)c, _loc_update.GetLocaleT()) )

            c = *p++;              /* skip whitespace */

 

//2. 不要期望能够 转换负负得正的字符串, 注意 "--100" 得到 0 ，  "-100" 得到 -100

        if(c == '-') {

            flags |= FL_NEG;       /* remember minus sign */

            c = *p++;

        }

        elseif (c == '+')

            c = *p++;              /* skip sign */

//3.  基数是 2 到 36 的闭区间 ， [2, 36]

        if(ibase < 0 || ibase == 1 || ibase > 36) {

            /* bad base! */

            if(endptr)

                /* store beginning of string in endptr */

                *endptr = nptr;

            return0L;              /* return 0 */

        }

 

//4. 如果转换的时候基数输入是0， 则基数取决于原字符的前面两个字符,

// 以非0开头的是 10进制字符串，

// 以0x或者0X开头的是 16进制字符串,

// 而仅仅以 0开头的是 8进制

        elseif (ibase == 0) {

            /* determine base free-lance, based on first two chars of

               string */

            if(c != '0')

                ibase = 10;

            elseif (*p == 'x'|| *p == 'X')

                ibase = 16;

            else

                ibase = 8;

        }

 

//  {{{   源码里面，这个地方 有这么一段 暂时不知道是干嘛的, 在我看来貌似是多余的

        if(ibase == 0) {

            /* determine base free-lance, based on first two chars of

               string */

            if(c != '0')

                ibase = 10;

            elseif (*p == 'x'|| *p == 'X')

                ibase = 16;

            else

                ibase = 8;

        }

//}}}

 

// 5. 如果是 16 进制，则跳过0x 或者 0X 的前缀

        if(ibase == 16) {

            /* we might have 0x in front of number; remove if there */

            if(c == '0' && (*p == 'x' || *p =='X')) {

                ++p;

                c = *p++;      /* advance past prefix */

            }

        }

 

// 6. 下面就是读取字符串，然后按照 local 解析应用的数值, 如果在转换过程中出现各种情况都会对标志位flags 进行标记

        /* if our number exceeds this, we will overflow on multiply */

        maxval = ULONG_MAX / ibase;

 

 

        for(;;) {      /* exit in middle of loop */

            /* convert c to value */

            if( __ascii_isdigit_l((int)(unsignedchar)c, _loc_update.GetLocaleT()) )

                digval = c -'0';

            elseif ( __ascii_isalpha_l((int)(unsignedchar)c, _loc_update.GetLocaleT()) )

                digval = __ascii_toupper(c) -'A' + 10;

            else

                break;

            if(digval >= (unsigned)ibase)

                break;         /* exit loop if bad digit found */

 

            /* record the fact we have read one digit */

            flags |= FL_READDIGIT;

 

            /* we now need to compute number = number * base + digval,

               but we need to know if overflow occured.  This requires

               a tricky pre-check. */

 

            if(number < maxval || (number == maxval &&

                        (unsignedlong)digval <= ULONG_MAX % ibase)) {

                /* we won't overflow, go ahead and multiply */

                number = number * ibase + digval;

            }

            else{

                /* we would have overflowed -- set the overflow flag */

                flags |= FL_OVERFLOW;

                if(endptr == NULL) {

                    /* no need to keep on parsing if we

                       don't have to return the endptr. */

                    break;

                }

            }

 

            c = *p++;              /* read next digit */

        }

 

        --p;                           /* point to place that stopped scan */

 

        if(!(flags & FL_READDIGIT)) {

            /* no number there; return 0 and point to beginning of

               string */

            if(endptr)

                /* store beginning of string in endptr later on */

                p = nptr;

            number = 0L;           /* return 0 */

        }

        elseif ( (flags & FL_OVERFLOW) ||

                ( !(flags & FL_UNSIGNED) &&

                  ( ( (flags & FL_NEG) && (number > -LONG_MIN) ) ||

                    ( !(flags & FL_NEG) && (number > LONG_MAX) ) ) ) )

        {

            /* overflow or signed overflow occurred */

            errno= ERANGE;                  //(老的实现方式和新的实现方式区别主要在这里, 新版友记录转换过程)

            if( flags & FL_UNSIGNED )

                number = ULONG_MAX;

            elseif ( flags & FL_NEG )

                number = (unsignedlong)(-LONG_MIN);

            else

                number = LONG_MAX;

        }

 

        if(endptr != NULL)

            /* store pointer to char that stopped the scan */

            *endptr = p;

 

        if(flags & FL_NEG)

            /* negate result if there was a neg sign */

            number = (unsignedlong)(-(long)number);

 

        returnnumber;                  /* done. */

}

 

 

所以 atoi 已经等同于strtol 

Sign,  Clown , 2010.07.01 . 23:32 . HDPY

[本文原创，转载请注明出处，在文章末尾提供原文链接http://www.cnblogs.com/JefferyZhou/，否则一旦发现，将按字节每人民币收费，绝不论价]