一个StringBuilder的C++实现

StringBuilder.h 头文件清单

#ifndef _StringBuilder_H_#define _StringBuilder_H_#include <list>#include <string>// Subset of http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspxtemplate <typename chr>class StringBuilder {	typedef std::basic_string<chr> string_t;	typedef std::list<string_t> container_t; // Reasons not to use vector below.	typedef typename string_t::size_type size_type; // Reuse the size type in the string.	container_t m_Data;	size_type m_totalSize;	void append(const string_t &src) {		m_Data.push_back(src);		m_totalSize += src.size();	}	// No copy constructor, no assignment.	StringBuilder(const StringBuilder &);	StringBuilder & Operator = (const StringBuilder &);public:	StringBuilder(const string_t &src) {		if (!src.empty()) {			m_Data.push_back(src);		}		m_totalSize = src.size();	}	StringBuilder() {		m_totalSize = 0;	}	// TODO: Constructor that takes an array of strings.	StringBuilder & Append(const string_t &src) {		append(src);		return *this; // allow chaining.	}	// This one lets you add any STL container to the string builder.	template<class inputIterator>	StringBuilder & Add(const inputIterator &first, const inputIterator &afterLast) {		// std::for_each and a lambda look like overkill here.		// <b>Not</b> using std::copy, since we want to update m_totalSize too.		for (inputIterator f = first; f != afterLast; ++f) {			append(*f);		}		return *this; // allow chaining.	}	StringBuilder & AppendLine(const string_t &src) {		static chr lineFeed[] { 10, 0 }; // C++ 11. Feel the love!		m_Data.push_back(src + lineFeed);		m_totalSize += 1 + src.size();		return *this; // allow chaining.	}	StringBuilder & AppendLine() {		static chr lineFeed[] { 10, 0 };		m_Data.push_back(lineFeed);		++m_totalSize;		return *this; // allow chaining.	}	// TODO: AppendFormat implementation. Not relevant for the article.	// Like C# StringBuilder.ToString()	// Note the use of reserve() to avoid reallocations.	string_t ToString() const {		string_t result;		// The whole point of the exercise!		// If the container has a lot of strings, reallocation (each time the result grows) will take a serious toll,		// both in performance and chances of failure.		// I measured (in code I cannot publish) fractions of a second using 'reserve', and almost two minutes using +=.		result.reserve(m_totalSize + 1);		// result = std::accumulate(m_Data.begin(), m_Data.end(), result); // This would lose the advantage of 'reserve'		for (auto iter = m_Data.begin(); iter != m_Data.end(); ++iter) {			result += *iter;		}		return result;	}	// like javascript Array.join()	string_t Join(const string_t &delim) const {		if (delim.empty()) {			return ToString();		}		string_t result;		if (m_Data.empty()) {			return result;		}		// Hope we don't overflow the size type.		size_type st = (delim.size() * (m_Data.size() - 1)) + m_totalSize + 1;		result.reserve(st);		// If you need reasons to love C++11, here is one.		struct adder {			string_t m_Joiner;			adder(const string_t &s) : m_Joiner(s) {				// This constructor is NOT empty.			}			// This functor runs under accumulate() without reallocations, if 'l' has reserved enough memory.			string_t operator()(string_t &l, const string_t &r) {				l += m_Joiner;				l += r;				return l;			}		} adr(delim);		auto iter = m_Data.begin();		// Skip the delimiter before the first element in the container.		result += *iter;		return std::accumulate(++iter, m_Data.end(), result, adr);	}}; // class StringBuilder#endif // !_StringBuilder_H_
 
如何使用，示例代码段
#include "StringBuilder.h"#include <iostream>int main(int argc, char *argv[]){	StringBuilder<char> ansi;	ansi.Append("Hello").Append(" ").AppendLine("World");	std::cout << ansi.ToString();	std::cin.get();	return 0;}