tinyxml2-day02-[class StrPair]

StrPair类提供了对一个字符串的一些操作，可以将目标字符串存储到类内，通过存储目标字符串的起始地址和结束地址。
StrPair类提供了一个flag，可以通过对flag赋值，来对当前字符串进行相应的操作。
针对xml文件，StrPair类提供了读取标题和内容的函数。（这里不太确定，需要等到后面查看这两个函数的用法才知道，从函数的实现上看，的确是这样的）
StrPair将它的拷贝构造函数和赋值构造函数，都声明称私有的，避免使用这两种构造，StrPair内还有两个指针类型的成员变量，如果使用这两种构造，就不得不考虑深拷贝。
StrPair提供了一个获取字符串的成员函数，该函数中，将一些特殊字符做了处理，然后再将字符串输出，至于如何处理，还是要看具体实现。
StrPair定义如下：

class TINYXML2_LIB StrPair
{
public:
    enum {
        NEEDS_ENTITY_PROCESSING			= 0x01,
        NEEDS_NEWLINE_NORMALIZATION		= 0x02,
        NEEDS_WHITESPACE_COLLAPSING     = 0x04,

        TEXT_ELEMENT		            = NEEDS_ENTITY_PROCESSING | NEEDS_NEWLINE_NORMALIZATION,
        TEXT_ELEMENT_LEAVE_ENTITIES		= NEEDS_NEWLINE_NORMALIZATION,
        ATTRIBUTE_NAME		            = 0,
        ATTRIBUTE_VALUE		            = NEEDS_ENTITY_PROCESSING | NEEDS_NEWLINE_NORMALIZATION,
        ATTRIBUTE_VALUE_LEAVE_ENTITIES  = NEEDS_NEWLINE_NORMALIZATION,
        COMMENT							= NEEDS_NEWLINE_NORMALIZATION
    };

    StrPair() : _flags( 0 ), _start( 0 ), _end( 0 ) {}
    ~StrPair();

    void Set( char* start, char* end, int flags ) {
        TIXMLASSERT( start );
        TIXMLASSERT( end );
        Reset();
        _start  = start;
        _end    = end;
        _flags  = flags | NEEDS_FLUSH;
    }

    const char* GetStr();

    bool Empty() const {
        return _start == _end;
    }

    void SetInternedStr( const char* str ) {
        Reset();
        _start = const_cast(str);
    }

    void SetStr( const char* str, int flags=0 );

    char* ParseText( char* in, const char* endTag, int strFlags, int* curLineNumPtr );
    char* ParseName( char* in );

    void TransferTo( StrPair* other );
	void Reset();

private:
    void CollapseWhitespace();

    enum {
        NEEDS_FLUSH = 0x100,
        NEEDS_DELETE = 0x200
    };

    int     _flags;
    char*   _start;
    char*   _end;

    StrPair( const StrPair& other );	// not supported
    void operator=( const StrPair& other );	// not supported, use TransferTo()
};

以下，是StrPair类的实现部分：

StrPair::~StrPair()
{
    Reset();
}


void StrPair::TransferTo( StrPair* other )
{
    if ( this == other ) {
        return;
    }
    // This in effect implements the assignment operator by "moving"
    // ownership (as in auto_ptr).

    TIXMLASSERT( other != 0 );
    TIXMLASSERT( other->_flags == 0 );
    TIXMLASSERT( other->_start == 0 );
    TIXMLASSERT( other->_end == 0 );

    other->Reset();

    other->_flags = _flags;
    other->_start = _start;
    other->_end = _end;

    _flags = 0;
    _start = 0;
    _end = 0;
}


void StrPair::Reset()
{
    if ( _flags & NEEDS_DELETE ) {
        delete [] _start;
    }
    _flags = 0;
    _start = 0;
    _end = 0;
}


void StrPair::SetStr( const char* str, int flags )
{
    TIXMLASSERT( str );
    Reset();
    size_t len = strlen( str );
    TIXMLASSERT( _start == 0 );
    _start = new char[ len+1 ];
    memcpy( _start, str, len+1 );
    _end = _start + len;
    _flags = flags | NEEDS_DELETE;
}


char* StrPair::ParseText( char* p, const char* endTag, int strFlags, int* curLineNumPtr )
{
    TIXMLASSERT( p );
    TIXMLASSERT( endTag && *endTag );
	TIXMLASSERT(curLineNumPtr);

    char* start = p;
    const char  endChar = *endTag;
    size_t length = strlen( endTag );

    // Inner loop of text parsing.
    while ( *p ) {
        if ( *p == endChar && strncmp( p, endTag, length ) == 0 ) {
            Set( start, p, strFlags );
            return p + length;
        } else if (*p == '\n') {
            ++(*curLineNumPtr);
        }
        ++p;
        TIXMLASSERT( p );
    }
    return 0;
}


char* StrPair::ParseName( char* p )
{
    if ( !p || !(*p) ) {
        return 0;
    }
    if ( !XMLUtil::IsNameStartChar( *p ) ) {
        return 0;
    }

    char* const start = p;
    ++p;
    while ( *p && XMLUtil::IsNameChar( *p ) ) {
        ++p;
    }

    Set( start, p, 0 );
    return p;
}


void StrPair::CollapseWhitespace()
{
    // Adjusting _start would cause undefined behavior on delete[]
    TIXMLASSERT( ( _flags & NEEDS_DELETE ) == 0 );
    // Trim leading space.
    _start = XMLUtil::SkipWhiteSpace( _start, 0 );

    if ( *_start ) {
        const char* p = _start;	// the read pointer
        char* q = _start;	// the write pointer

        while( *p ) {
            if ( XMLUtil::IsWhiteSpace( *p )) {
                p = XMLUtil::SkipWhiteSpace( p, 0 );
                if ( *p == 0 ) {
                    break;    // don't write to q; this trims the trailing space.
                }
                *q = ' ';
                ++q;
            }
            *q = *p;
            ++q;
            ++p;
        }
        *q = 0;
    }
}


const char* StrPair::GetStr()
{
    TIXMLASSERT( _start );
    TIXMLASSERT( _end );
    if ( _flags & NEEDS_FLUSH ) {
        *_end = 0;
        _flags ^= NEEDS_FLUSH;

        if ( _flags ) {
            const char* p = _start;	// the read pointer
            char* q = _start;	// the write pointer

            while( p < _end ) {
                if ( (_flags & NEEDS_NEWLINE_NORMALIZATION) && *p == CR ) {
                    // CR-LF pair becomes LF
                    // CR alone becomes LF
                    // LF-CR becomes LF
                    if ( *(p+1) == LF ) {
                        p += 2;
                    }
                    else {
                        ++p;
                    }
                    *q = LF;
                    ++q;
                }
                else if ( (_flags & NEEDS_NEWLINE_NORMALIZATION) && *p == LF ) {
                    if ( *(p+1) == CR ) {
                        p += 2;
                    }
                    else {
                        ++p;
                    }
                    *q = LF;
                    ++q;
                }
                else if ( (_flags & NEEDS_ENTITY_PROCESSING) && *p == '&' ) {
                    // Entities handled by tinyXML2:
                    // - special entities in the entity table [in/out]
                    // - numeric character reference [in]
                    //   中 or 中

                    if ( *(p+1) == '#' ) {
                        const int buflen = 10;
                        char buf[buflen] = { 0 };
                        int len = 0;
                        const char* adjusted = const_cast( XMLUtil::GetCharacterRef( p, buf, &len ) );
                        if ( adjusted == 0 ) {
                            *q = *p;
                            ++p;
                            ++q;
                        }
                        else {
                            TIXMLASSERT( 0 <= len && len <= buflen );
                            TIXMLASSERT( q + len <= adjusted );
                            p = adjusted;
                            memcpy( q, buf, len );
                            q += len;
                        }
                    }
                    else {
                        bool entityFound = false;
                        for( int i = 0; i < NUM_ENTITIES; ++i ) {
                            const Entity& entity = entities[i];
                            if ( strncmp( p + 1, entity.pattern, entity.length ) == 0
                                    && *( p + entity.length + 1 ) == ';' ) {
                                // Found an entity - convert.
                                *q = entity.value;
                                ++q;
                                p += entity.length + 2;
                                entityFound = true;
                                break;
                            }
                        }
                        if ( !entityFound ) {
                            // fixme: treat as error?
                            ++p;
                            ++q;
                        }
                    }
                }
                else {
                    *q = *p;
                    ++p;
                    ++q;
                }
            }
            *q = 0;
        }
        // The loop below has plenty going on, and this
        // is a less useful mode. Break it out.
        if ( _flags & NEEDS_WHITESPACE_COLLAPSING ) {
            CollapseWhitespace();
        }
        _flags = (_flags & NEEDS_DELETE);
    }
    TIXMLASSERT( _start );
    return _start;
}