QString CString char三者转换

转自：http://hi.baidu.com/koko200147/blog/item/7e3cad828c9b9bb66d8119cb.html
qstring is unicode. utf16 in qt4.

QString fromAscii ( const char * str, int size = -1 )
QString fromLatin1 ( const char * str, int size = -1 )
QString fromLocal8Bit ( const char * str, int size = -1 )
QString fromRawData ( const QChar * unicode, int size )
QString fromStdString ( const std::string & str )
QString fromStdWString ( const std::wstring & str )
QString fromUcs4 ( const uint * unicode, int size = -1 )
QString fromUtf8 ( const char * str, int size = -1 )
QString fromUtf16 ( const ushort * unicode, int size = -1 )
QString fromWCharArray ( const wchar_t * string, int size = -1 )

qstring ->std::string
qstring::toStdString () ,qstring::toStdWString ()

BSTR<->qstring
BSTR bstr_str;
qstring q_str((QChar*)bstr_str, wcslen(bstr_str))
bstr_str = SysAllocString(q_str.utf16())

remember use SysFreeString on BSTR

qstring<->LPCSTR
qstring::toLocal8Bit().constData()
QString fromLocal8Bit ( const char * str, int size = -1 )

qstring<->LPCWSTR
qstring::utf16()
QString fromUtf16 ( const ushort * unicode, int size = -1 )

qstring<->CString
CString c_str(qstring::utf16())
QString fromUtf16 (LPCTSTR(c_str) )

传给未分配内存的const char* （LPCTSTR）指针.
   CString cstr(asdd);
   const char* ch = (LPCTSTR)cstr;
   ch指向的地址和cstr相同。但由于使用const保证ch不会修改，所以安全.2.传给未分配内存的指

针.
    CString cstr = "ASDDSD";
    char *ch = cstr.GetBuffer(cstr1.GetLength() + 1);
    cstr.ReleaseBuffer();
    //修改ch指向的值等于修改cstr里面的值.
    //PS:用完ch后,不用delete ch,因为这样会破坏cstr内部空间,容易造成程序崩溃.
3.第二种用法。把CString 值赋给已分配内存的char *。
    CString cstr1 = "ASDDSD";
    int strLength = cstr1.GetLength() + 1;
    char *pValue = new char[strLength];
    strncpy(pValue, cstr1, strLength);
4.第三种用法.把CString 值赋给已分配内存char[]数组.
    CString cstr2 = "ASDDSD";
    int strLength1 = cstr1.GetLength() + 1;
    char chArray[100];
    memset(chArray,0, sizeof(bool) * 100); //将数组的垃圾内容清空.
    strncpy(chArray, cstr1, strLength1);
如果上述都不行：
CString转换为char*
        CString origCString("Hello, World!");
        wchar_t* wCharString = origCString.GetBuffer(origCString.GetLength()+1);
        size_t origsize = wcslen(wCharString) + 1;
        size_t convertedChars = 0;
        char *CharString;
        CharString=new char(origsize);
        wcstombs_s(&convertedChars, CharString, origsize, wCharString , _TRUNCATE);
        cout << CharString << endl;
成功输出字符串"Hello,World"
原因：
原来在VC++ 2005以前，应用程序默认都是关闭对Unicode的支持的，而在VC2005中，默认打开了对

它的支持，CString对应的字符串应该是TCHAR，TCHAR的定义是这样的，
        #ifdef _UNICODE
        typedef wchar_t TCHAR    ;
        #else
        typedef char TCHAR;
        #endif
所以在工程中应该可以关闭对于Unicode的支持，从而可以直接转换。这个做法是右击工程名—〉

Property—〉General中的character set中选择notset，这样，本文开头的那段代码就可以正确的

执行了。
QString GB_To_Utf8(char *strText)
{
    return QString::fromLocal8Bit(strText);
}

如何将QString转换为char *或者相反
 
How can I convert a QString to char* and vice versa ?(trolltech)
Answer:
In order to convert a QString to a char*, then you first need to get a latin1

representation of the string by calling toLatin1() on it which will return a

QByteArray. Then call data() on the QByteArray to get a pointer to the data stored in

the byte array. See the documentation:
See the following example for a demonstration:
int main(int argc, char **argv)
{
QApplication app(argc, argv);
QString str1 = "Test";
QByteArray ba = str1.toLatin1();
const char *c_str2 = ba.data();
printf("str2: %s", c_str2);
return app.exec(); 
}
Note that it is necessary to store the bytearray before you call data() on it, a call

like the following
const char *c_str2 = str2.toLatin1().data();
will make the application crash as the QByteArray has not been stored and hence no

longer exists.

To convert a char* to a QString you can use the QString constructor that takes a

QLatin1String, e.g:
QString string = QString(QLatin1String(c_str2)) ;
 
还有其他多种方法：
方法一 -----------------------------------------
#define G2U(s) ( QTextCodec::codecForName("GBK")->toUnicode(s) )
#define U2G(s) ( QTextCodec::codecForName("GBK")->fromUnicode(s) )
QString str;
QCString cstr;
str = G2U("中文输入");
cstr = U2G(str);
QCString有这样一个重载运算符
operator const char * () const
可以这样
printf("%s\n", (const char*) cstr);
或是copy出来
char buf[1024];
strcpy(buf, (const char*) cstr);
 
方法二 -----------------------------------------
如果是中文系统
直接用   (const char*) str.local8Bit()
例如
printf("%s", (const char*) str.local8Bit());
str是一个QString
方法三 -----------------------------------------
char str[64];
QTextCodec *textcod = QTextCodec::codecForName("GBK");
        QCString string1 = textcod ->fromUnicode(listbox1->currentText());
        strcpy(str,string1);
QString和Std::string
从char*到 QString可以从fromLocal8Bit()转化
std::string有c_str()的函数使再转化为char*
QString有toAscii()记不清了

你可以看看.

又是我的粗心酿成大错，我重新查看了一下Qt文档，原来Qt可以直接从std::wstring产生一个

QString，用 QString::fromStdWString(const std::wstring &)这个静态成员函数即可。我试了试

用std::string的c_str()返回的char *构造的QString不能再保存原先的中文信息，而用

std::wstring构造的QString则可以用qDebug()输出原先的中文信息
GB编码与UTF8编码的转换
在主函数app后加上这句：
QTextCodec::setCodecForLocale(QTextCodec::codecForName("GB18030"));
 
然后是从UTF8编码到GB编码的字符串转换方法：
QString Utf8_To_GB(QString strText)
{
    return QString::fromUtf8(strText.toLocal8Bit().data());
}
 
至于从GB到UTF8，那大家就经常用了：