MongoDB代碼中的StringBuilder類

MongoDB代碼中的StringBuilder類，學習下。

// stringdata.h/*    Copyright 2010 10gen Inc. * *    Licensed under the Apache License, Version 2.0 (the "License"); *    you may not use this file except in compliance with the License. *    You may obtain a copy of the License at * *    http://www.apache.org/licenses/LICENSE-2.0 * *    Unless required by applicable law or agreed to in writing, software *    distributed under the License is distributed on an "AS IS" BASIS, *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *    See the License for the specific language governing permissions and *    limitations under the License. */#ifndef BSON_STRINDATA_HEADER#define BSON_STRINDATA_HEADER#include <string>#include <cstring>namespace mongo {    using std::string;    // A StringData object wraps a 'const string&' or a 'const char*' without    // copying its contents. The most common usage is as a function argument that    // takes any of the two forms of strings above. Fundamentally, this class tries    // go around the fact that string literals in C++ are char[N]'s.    //    // Note that the object StringData wraps around must be alive while the StringDAta    // is.    class StringData {    public:        // Construct a StringData explicilty, for the case where the lenght of        // string is not known. 'c' must be a pointer to a null-terminated string.        StringData( const char* c )            : _data(c), _size((unsigned) strlen(c)) {}        // Construct a StringData explicitly, for the case where the length of the string        // is already known. 'c' must be a pointer to a null-terminated string, and strlenOfc        // must be the length that std::strlen(c) would return, a.k.a the index of the        // terminator in c.        StringData( const char* c, size_t strlenOfc )            : _data(c), _size((unsigned) strlenOfc) {}        // Construct a StringData explicitly, for the case of a std::string.        StringData( const string& s )            : _data(s.c_str()), _size((unsigned) s.size()) {}        // Construct a StringData explicitly, for the case of a literal whose size is        // known at compile time.        struct LiteralTag {};        template<size_t N>        StringData( const char (&val)[N], LiteralTag )            : _data(&val[0]), _size(N-1) {}        // accessors        const char* const data() const { return _data; }        const unsigned size() const { return _size; }    private:        // There are two assumptions we use bellow.        // '_data' *always* finishes with a null terminator        // 'size' does *not* account for the null terminator        // These assumptions may make it easier to minimize changes to existing code.        const char* const _data;        const unsigned    _size;    };} // namespace mongo#endif  // BSON_STRINGDATA_HEADER

/* builder.h *//*    Copyright 2009 10gen Inc. * *    Licensed under the Apache License, Version 2.0 (the "License"); *    you may not use this file except in compliance with the License. *    You may obtain a copy of the License at * *    http://www.apache.org/licenses/LICENSE-2.0 * *    Unless required by applicable law or agreed to in writing, software *    distributed under the License is distributed on an "AS IS" BASIS, *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *    See the License for the specific language governing permissions and *    limitations under the License. */#pragma once#include <string>#include <string.h>#include <stdio.h>#include <boost/shared_ptr.hpp>#include "../inline_decls.h"#include "../stringdata.h"namespace mongo {    /* Note the limit here is rather arbitrary and is simply a standard. generally the code works       with any object that fits in ram.       Also note that the server has some basic checks to enforce this limit but those checks are not exhaustive       for example need to check for size too big after         update $push (append) operation         various db.eval() type operations    */    const int BSONObjMaxUserSize = 16 * 1024 * 1024;    /*       Sometimeswe we need objects slightly larger - an object in the replication local.oplog       is slightly larger than a user object for example.    */    const int BSONObjMaxInternalSize = BSONObjMaxUserSize + ( 16 * 1024 );    const int BufferMaxSize = 64 * 1024 * 1024;    class StringBuilder;    void msgasserted(int msgid, const char *msg);    class BufBuilder {    public:        BufBuilder(int initsize = 512) : size(initsize) {            if ( size > 0 ) {                data = (char *) malloc(size);                if( data == 0 )                    msgasserted(10000, "out of memory BufBuilder");            }            else {                data = 0;            }            l = 0;        }        ~BufBuilder() {            kill();        }        void kill() {            if ( data ) {                free(data);                data = 0;            }        }        void reset( int maxSize = 0 ) {            l = 0;            if ( maxSize && size > maxSize ) {                free(data);                data = (char*)malloc(maxSize);                size = maxSize;            }        }        /** leave room for some stuff later            @return point to region that was skipped.  pointer may change later (on realloc), so for immediate use only        */        char* skip(int n) { return grow(n); }        /* note this may be deallocated (realloced) if you keep writing. */        char* buf() { return data; }        const char* buf() const { return data; }        /* assume ownership of the buffer - you must then free() it */        void decouple() { data = 0; }        void appendChar(char j) {            *((char*)grow(sizeof(char))) = j;        }        void appendNum(char j) {            *((char*)grow(sizeof(char))) = j;        }        void appendNum(short j) {            *((short*)grow(sizeof(short))) = j;        }        void appendNum(int j) {            *((int*)grow(sizeof(int))) = j;        }        void appendNum(unsigned j) {            *((unsigned*)grow(sizeof(unsigned))) = j;        }        void appendNum(bool j) {            *((bool*)grow(sizeof(bool))) = j;        }        void appendNum(double j) {            *((double*)grow(sizeof(double))) = j;        }        void appendNum(long long j) {            *((long long*)grow(sizeof(long long))) = j;        }        void appendNum(unsigned long long j) {            *((unsigned long long*)grow(sizeof(unsigned long long))) = j;        }        void appendBuf(const void *src, size_t len) {            memcpy(grow((int) len), src, len);        }        template<class T>        void appendStruct(const T& s) {            appendBuf(&s, sizeof(T));        }        void appendStr(const StringData &str , bool includeEOO = true ) {            const int len = str.size() + ( includeEOO ? 1 : 0 );            memcpy(grow(len), str.data(), len);        }        int len() const { return l; }        void setlen( int newLen ) { l = newLen; }        int getSize() const { return size; }        /* returns the pre-grow write position */        inline char* grow(int by) {            int oldlen = l;            l += by;            if ( l > size ) {                grow_reallocate();            }            return data + oldlen;        }    private:        /* "slow" portion of 'grow()'  */        void NOINLINE_DECL grow_reallocate() {            int a = size * 2;            if ( a == 0 )                a = 512;            if ( l > a )                a = l + 16 * 1024;            if ( a > BufferMaxSize )                msgasserted(13548, "BufBuilder grow() > 64MB");            data = (char *) realloc(data, a);            size= a;        }        char *data;        int l;        int size;        friend class StringBuilder;    };#if defined(_WIN32)#pragma warning( push )// warning C4996: 'sprintf': This function or variable may be unsafe. Consider using sprintf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.#pragma warning( disable : 4996 )#endif    /** stringstream deals with locale so this is a lot faster than std::stringstream for UTF8 */    class StringBuilder {    public:        StringBuilder( int initsize=256 )            : _buf( initsize ) {        }        StringBuilder& operator<<( double x ) {            return SBNUM( x , 25 , "%g" );        }        StringBuilder& operator<<( int x ) {            return SBNUM( x , 11 , "%d" );        }        StringBuilder& operator<<( unsigned x ) {            return SBNUM( x , 11 , "%u" );        }        StringBuilder& operator<<( long x ) {            return SBNUM( x , 22 , "%ld" );        }        StringBuilder& operator<<( unsigned long x ) {            return SBNUM( x , 22 , "%lu" );        }        StringBuilder& operator<<( long long x ) {            return SBNUM( x , 22 , "%lld" );        }        StringBuilder& operator<<( unsigned long long x ) {            return SBNUM( x , 22 , "%llu" );        }        StringBuilder& operator<<( short x ) {            return SBNUM( x , 8 , "%hd" );        }        StringBuilder& operator<<( char c ) {            _buf.grow( 1 )[0] = c;            return *this;        }        void appendDoubleNice( double x ) {            int prev = _buf.l;            char * start = _buf.grow( 32 );            int z = sprintf( start , "%.16g" , x );            assert( z >= 0 );            _buf.l = prev + z;            if( strchr(start, '.') == 0 && strchr(start, 'E') == 0 && strchr(start, 'N') == 0 ) {                write( ".0" , 2 );            }        }        void write( const char* buf, int len) { memcpy( _buf.grow( len ) , buf , len ); }        void append( const StringData& str ) { memcpy( _buf.grow( str.size() ) , str.data() , str.size() ); }        StringBuilder& operator<<( const StringData& str ) {            append( str );            return *this;        }        void reset( int maxSize = 0 ) { _buf.reset( maxSize ); }        std::string str() const { return std::string(_buf.data, _buf.l); }    private:        BufBuilder _buf;        // non-copyable, non-assignable        StringBuilder( const StringBuilder& );        StringBuilder& operator=( const StringBuilder& );        template <typename T>        StringBuilder& SBNUM(T val,int maxSize,const char *macro)  {            int prev = _buf.l;            int z = sprintf( _buf.grow(maxSize) , macro , (val) );            assert( z >= 0 );            _buf.l = prev + z;            return *this;        }    };#if defined(_WIN32)#pragma warning( pop )#endif} // namespace mongo