UTF8与ANSI等编码间如何转换，在C++有API吗?

#1

MultiByteWideChar(CP_UTF8,0,...);
WideCharToMultiByte(CP_UTF8,0,...);

#2

以前写的两个函数，可以参考一下，具体可以查看WideCharToMultiByte和MultiByteToWideChar函数的使用：
//====Unicode—>简体中文
CString CCodeTransDlg::UnicodeToJt(CString str) const
{
CString csSub;
int iLen = strlen(str) / 4;//简体中文的长度
int iRealLen=0; //对应中文的实际长度
WCHAR *uUnicode = new WCHAR[iLen];//unicode的十进制数组

for (int li=0; li<iLen; li++)
{
csSub = str.Mid(li*4, 4);
uUnicode[li] = StrHexToDec(csSub);
if (uUnicode[li]<256) iRealLen +=1;
else iRealLen +=2;
}

CString des;
WideCharToMultiByte(936, 0, uUnicode, -1, des.GetBuffer(iRealLen), iRealLen, NULL, NULL);
des.ReleaseBuffer(iRealLen);

delete[] uUnicode;
return des;
}//====简体—>DBCS码
CString CCodeTransDlg::JtToDBCS(CString str) const
{
CString csTmp,csResult="";
byte tmp;
for (int li=0; li<str.GetLength(); li++)
{
tmp = str[li];
csTmp.Format("%x", tmp);
csResult += csTmp;
}

return csResult;
}

#3

ansi在win平台他会自动在后台把两个字节组合例如char*str="中国";
输出就可以看到中文
utf-8转换到ANSI这个问题我也在做我是这样做的
utf-8 <---->unicode <------>ansi

unsigned int utf82unicode(long utf8){
         unsigned  int unicode=0;
         if((0x00000000<utf8)&&(utf8<0x0000007F)){        /* 0xxxxxxx  */
                unicode=(unsigned int)utf8;
                return unicode;
         }else{
                if((0x0000C080<utf8)&&(utf8<0x0000DFBF)){ /* 110xxxxx 10xxxxxx  */
                       unicode=(unsigned int)(0x00001F00&utf8)>>2
                               |(unsigned int)(0x0000003F&utf8);
                       return unicode;
                }else{
                      if((0x00E08080<utf8)&&(utf8<0x00EFBFBF)){ /* 1110xxxx 10xxxxxx 10xxxxxx  */
                             unicode=(unsigned int)(0x000F0000&utf8)>>4
                                     |(unsigned int)(0x00003F00&utf8)>>2
                                     |(unsigned int)(0x0000003F&utf8);
                                     return unicode;
                      }else{
                            if((0xF0808080<utf8)&&(utf8<0xF7BFBFBF))
                            /*11110xxx 10xxxxxx 10xxxxxx 10xxxxxx */
                                  unicode=(unsigned int)(0x07000000&utf8)>>6
                                          |(unsigned int)(0x003F0000&utf8)>>4
                                          |(unsigned int)(0x00003F00&utf8)>>2
                                          |(unsigned int)(0x0000003F&utf8);
                                  return unicode;
                      }

                }

         }
}
void printNumber(long i){
     cout<<"In printNumber's input "<<hex<<i<<endl;
     char buffer [sizeof(long)*8+1];
     ltoa (i,buffer,10);
     printf ("decimal: %s\n",buffer);
     ltoa (i,buffer,16);
     printf ("hexadecimal: %s\n",buffer);
     ltoa (i,buffer,2);
     printf ("binary: %s\n",buffer);
     return ;
}
unsigned int u2utf8(unsigned short uni)
{
unsigned int utf8;
if(uni < 0x80)
{
utf8 = uni;
return utf8;
}
if(uni < 0x800)
{
utf8 = (0xc0 | (uni >> 6)) << 8
| (0x80 | (uni & 0x3f));

return utf8;
}
if(uni < 0x10000)
{
utf8 = (0xe0 | (uni>>12)) << 16
| (0x80 | (uni >> 6 & 0x3f)) << 8
| (0x80 | (uni & 0x3f));
return utf8;
}
if(uni < 0x20000)
{
utf8 = (0xf0 | (uni >> 18)) << 24
| (0x80 | (uni >> 12 & 0x3f)) << 16
| (0x80 | (uni >> 6 & 0x3f)) << 8
| (0x80 | (uni & 0x3f));
return utf8;
}
else
{
/*we don't deal with it, so we return the unicode.*/
return uni;
}

}
哈哈!
utf82unicode没有实现全部的utf-8到unicode的转换
只做了四字节的utf-8到unicode的转换!

#4

我有个问题不明白,在char *str="汉"里面,用的是什么编码?是ASCII编码还是ANSI(GB2312)?我试了一下楼上的函数,从Unicode转换到ANSI时,得到的不是ANSI编码(BA BA),而是ASCII编码(-70 -70).

#5

UTF-8只是对UNICODE的一个编码方案，不要和UNICODE混淆了，UTF-8和UNICODE之间只是一个对照关系，所以编码解码都很容易。
UNICODE和本地编码方案（如GB2312）之间的转换可以通过标准的API来实现：
wcstombs
mbstowcs
使用这两个函数之前必须将你的LC_CTYPE设置成你想要的本地编码方案（使用 setlocale函数）

上面这些都是标准C++的实现方式，和使用WIN32 API：WideCharToMultiByte相比更加通用。
配合“ 回复人：woundedsoul(浪子) ”提供的UTF-8与UNICODE之间的转换（他实现得不完整，楼主要注意）
就可以在GB和UTF-8之间随意操作了：）

#6

顺便帮你贴一个完整的UTF8到WCS的转换函数（SWI库里面的---实际上它是在APACHE的库里面的实现，不过是一个旧一些时候的版本了）
//  gUTFBytes
//      A list of counts of trailing bytes for each initial byte in the input.
//
//  gUTFOffsets
//      A list of values to offset each result char type, according to how
//      many source bytes when into making it.
//
//  gFirstByteMark
//      A list of values to mask onto the first byte of an encoded sequence,
//      indexed by the number of bytes used to create the sequence.

static const char gUTFBytes[256] =
    {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
        ,   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
        ,   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
        ,   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
        ,   3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5
    };

static const unsigned long gUTFOffsets[6] =
    {  0, 0x3080, 0xE2080, 0x3C82080, 0xFA082080, 0x82082080 };

static const unsigned char gFirstByteMark[7] =
    {  0x00, 0x00, 0xC0, 0xE0,
       0xF0, 0xF8, 0xFC };

SWIcharResult SWIutf8towcs( const unsigned char *src, wchar_t *dst, int maxdstlen )
{
    // Get pointers to our start and end points of the input buffer
    const unsigned char* srcPtr = src;
    const unsigned char* srcEnd = src + strlen((const char *)src);
    wchar_t *dstSave = dst;
    wchar_t *dstEnd = dst+maxdstlen;  /* leave room for null */

    //  We now loop until we run out of input data.
    while (srcPtr < srcEnd) {
        unsigned int trailingBytes;
        unsigned long tmpVal = 0;

        // Get the next leading byte out
        const unsigned char firstByte = (unsigned char) *srcPtr;

        // Special-case ASCII, which is a leading byte value of <= 127
        if (firstByte <= 127) {
            *dst++ = (wchar_t) firstByte;
            srcPtr++;
            continue;
        }

        // See how many trailing src bytes this sequence is going to require
        trailingBytes = gUTFBytes[firstByte];

        //  If there are not enough source bytes to do this one, then we
        //  are done. Note that we done >= here because we are implicitly
        //  counting the 1 byte we get no matter what.
        if (srcPtr + trailingBytes >= srcEnd)
            return SWIchar_FAIL;  // ??

        // Looks ok, so lets build up the value
        switch (trailingBytes) {
        case 5: tmpVal += *srcPtr++; tmpVal <<= 6;
        case 4: tmpVal += *srcPtr++; tmpVal <<= 6;
        case 3: tmpVal += *srcPtr++; tmpVal <<= 6;
        case 2: tmpVal += *srcPtr++; tmpVal <<= 6;
        case 1: tmpVal += *srcPtr++; tmpVal <<= 6;
        case 0: tmpVal += *srcPtr++;
            break;
        default:
            return SWIchar_ERROR;
        }
        tmpVal -= gUTFOffsets[trailingBytes];

        // If surrogate pairs would be required for 16-bit characters, fail.
        if (tmpVal & 0xFFFF0000)
            return SWIchar_FAIL;

        if ( dst >= dstEnd ) {
            return SWIchar_BUFFER_OVERFLOW;
        }

        *dst++ = (wchar_t)tmpVal;
    }

    *dst = L'\0';

    // return dst-dstSave;

    return SWIchar_SUCCESS;   // check this (CARO)
}

#7

再BTW：将ANSI和GB2312混为一谈的话，在文化大革命时期是要抓出去砍头的，楼主犯了严重的政治错位，请google一下ANSI到底是什么，GB2312又是什么。

#8

在 C++ 中，将字符与字节进行转换的方法是：mbstowcs
如果是在 Visual C++ 中，那么更好的方法是：MultiByteToWideChar

搂主可以将
ANSI（gb2312等，char[]） => UNICODE 字符串（wchar_t[]）

再将
UNICODE（wchar_t[]） => utf8（char[]）
（utf8 很简单，因此这一步操作也可以自己写代码完成）

关于概念，推荐文章：
http://www.regexlab.com/zh/encoding.htm

关于 utf8 的格式，推荐文章：
http://www.nk975.com/sswater/myref/index.asp?id=20

#9

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UTF8与ANSI等编码间如何转换，在C++有API吗?

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