前言：C中是没有string这个类的（或者说就没有类的概念），C++ STL中提供了关于字符串操作的一系列操作，包括定义初始化，字符串算法，迭代器等等的一系列内容。
下面是自己实现的一个简单的string类：
#include <iostream> #include <cstring> using namespace std; class String{ public: // 默认构造函数 String(const char* str = NULL); // 复制构造函数 String(const String &str); // 析构函数 ~String(); // 字符串连接 String operator+(const String & str); // 字符串赋值 String & operator=(const String &str); // 字符串赋值 String & operator=(const char* str); // 判断是否字符串相等 bool operator==(const String &str); // 获取字符串长度 int length(); // 求子字符串[start,start+n-1] String substr(int start, int n); // 重载输出 friend ostream & operator<<(ostream &o,const String &str); private: char* data; int size; }; // 构造函数 String::String(const char *str){ if(str == NULL){ data = new char[1]; data[0] = '\0'; size = 0; }//if else{ size = strlen(str); data = new char[size+1]; strcpy(data,str); }//else } // 复制构造函数 String::String(const String &str){ size = str.size; data = new char[size+1]; strcpy(data,str.data); } // 析构函数 String::~String(){ delete[] data; } // 字符串连接 String String::operator+(const String &str){ String newStr; //释放原有空间 delete[] newStr.data; newStr.size = size + str.size; newStr.data = new char[newStr.size+1]; strcpy(newStr.data,data); strcpy(newStr.data+size,str.data); return newStr; } // 字符串赋值 String & String::operator=(const String &str){ if(data == str.data){ return *this; }//if delete [] data; size = str.size; data = new char[size+1]; strcpy(data,str.data); return *this; } // 字符串赋值 String& String::operator=(const char* str){ if(data == str){ return *this; }//if delete[] data; size = strlen(str); data = new char[size+1]; strcpy(data,str); return *this; } // 判断是否字符串相等 bool String::operator==(const String &str){ return strcmp(data,str.data) == 0; } // 获取字符串长度 int String::length(){ return size; } // 求子字符串[start,start+n-1] String String::substr(int start, int n){ String newStr; // 释放原有内存 delete [] newStr.data; // 重新申请内存 newStr.data = new char[n+1]; for(int i = 0;i < n;++i){ newStr.data[i] = data[start+i]; }//for newStr.data[n] = '\0'; newStr.size = n; return newStr; } // 重载输出 ostream & operator<<(ostream &o, const String &str){ o<<str.data; return o; }然后是加载了迭代器的string：
#pragma once #ifndef MYSTD_STRING_H_EX #define MYSTD_STRING_H_EX #include<cassert> // assert #include<cstddef> // std::size_t,std::ptrdiff_t #include<memory> // std::allocator #include<cstdlib> // rand() #include<exception> // std::out_of_range #include<iostream> //basic_istream, basic_ostream #define MYSTD_BEGIN namespace mystd { #define MYSTD_END } // mystd #ifdef __cplusplus MYSTD_BEGIN / //随机访问迭代器 template<class random_access_iterator, class Value_type, class Reference,class Difference_type> class reverse_random_access_iterator{ public: typedef Value_type value_type; typedef value_type* pointer; typedef Reference reference; typedef Difference_type difference_type; typedef std::size_t size_type; typedef std::random_access_iterator_tag reverse_iterator_category; public: random_access_iterator iterator; typedef reverse_random_access_iterator self; public: reverse_random_access_iterator() { //default constructor } explicit reverse_random_access_iterator(const random_access_iterator& tmp):iterator(tmp) { //constructor } reverse_random_access_iterator(const self& tmp):iterator(tmp.iterator) { // copy constructor } template<class random_access_iterator, class Value_type, class Reference,class Difference_type> reverse_random_access_iterator(const reverse_random_access_iterator<random_access_iterator,Value_type,Reference,Difference_type>& obj) :iterator(obj.iterator) { // 此构造函数主要为了进行转换之用, //reverse_iterator转换为 const_reverse_iterator } self& operator = (const self& tmp) // 可以不定义，直接使用默认的函数 { iterator = tmp.iterator; return *this; } ~reverse_random_access_iterator() { // do nothing } self& operator ++ () { --iterator; return *this; } self operator ++ (int) { self tmp(*this); ++*this; return tmp; } self& operator -- () { ++iterator; return *this; } self operator -- (int) { self tmp(*this); --*this; return tmp; } self operator + (difference_type n) const { return self(iterator - n); } self operator - (difference_type n) const { return *this + (-n); } self& operator += (difference_type n) { iterator -= n; return *this; } self& operator -= (difference_type n) { iterator += n; return *this; } reference operator * () const { return *(iterator - 1); } bool operator == (const self& tmp) const { return iterator == tmp.iterator; } bool operator != (const self& tmp) const { return !(*this == tmp); } bool operator < (const self& tmp) const { return tmp.iterator < iterator; } bool operator <= (const self& tmp) const { return tmp.iterator <= iterator; } bool operator > (const self& tmp) const { return iterator < tmp.iterator; } bool operator >= (const self& tmp) const { return iterator <= tmp.iterator; } random_access_iterator base() const { return iterator; } friend difference_type operator - (const self& tmp_1,const self& tmp_2) { return tmp_2.iterator - tmp_1.iterator; } }; template<class T, class Reference,class Difference_type> class random_access_iterator{ // 反向随机访问迭代器 public: typedef T value_type; typedef value_type *pointer; typedef Reference reference; typedef Difference_type difference_type; typedef std::size_t size_type; typedef std::random_access_iterator_tag iterator_category; public: pointer ptr; typedef random_access_iterator self; public: random_access_iterator() { } explicit random_access_iterator(pointer tmp):ptr(tmp) { } random_access_iterator(const self& tmp):ptr(tmp.ptr) { } template<class T, class Reference,class Difference_type> random_access_iterator(const random_access_iterator<T,Reference,Difference_type>& obj) :ptr(obj.ptr) { // 此构造函数主要为了进行转换之用, //iterator转换为 const_iterator } self& operator = (const self& tmp) { ptr = tmp.ptr; return *this; } ~random_access_iterator() { } self& operator ++ () { ++ptr; return *this; } self operator ++ (int) { self tmp(*this); ++*this; return tmp; } self& operator -- () { --ptr; return *this; } self operator -- (int) { self tmp(*this); --*this; return tmp; } reference operator * () const // 足够的自由度 { return *ptr; } bool operator == (const self& tmp) const { return ptr == tmp.ptr; } bool operator != (const self& tmp) const { return !(*this == tmp); } bool operator < (const self& tmp) const { return ptr < tmp.ptr; } bool operator <= (const self& tmp) const { return ptr <= tmp.ptr; } bool operator > (const self& tmp) const { return tmp.ptr < ptr; } bool operator >= (const self& tmp) const { return tmp.ptr <= ptr; } self operator + (difference_type n) const { return self(ptr + n); } self operator - (difference_type n) const { return *this + (-n); } self& operator += (difference_type n) { ptr += n; return *this; } self& operator -= (difference_type n) { ptr -= n; return *this; } friend difference_type operator - (const self& tmp_1,const self& tmp_2) { return tmp_1.ptr - tmp_2.ptr; } }; //限于篇幅，这里的char_traits模板类用的是标准库的， //我的博客里有一篇文章是关于char_traits模板类的实现的，完全可以用在这里。 // template<class charT,class traits_type = std::char_traits<charT>,class Alloc = std::allocator<charT> > class basic_string { public: typedef mystd::random_access_iterator<charT,charT&,std::ptrdiff_t> iterator; typedef mystd::random_access_iterator<const charT,const charT&,std::ptrdiff_t> const_iterator; typedef mystd::reverse_random_access_iterator<iterator,charT,charT&,std::ptrdiff_t> reverse_iterator; typedef mystd::reverse_random_access_iterator<const_iterator,const charT,const charT&,std::ptrdiff_t> const_reverse_iterator; typedef typename iterator::value_type value_type; typedef typename iterator::reference reference; typedef typename iterator::pointer pointer; typedef typename iterator::size_type size_type; typedef typename iterator::difference_type difference_type; typedef typename iterator::iterator_category iterator_category; typedef typename const_iterator::reference const_reference; typedef typename const_iterator::pointer const_pointer; typedef Alloc allocator_type; public: static const size_type npos = size_type(-1); private: pointer start,finish,end_of_storage; //数据成员 typedef basic_string self; //私有类型 allocator_type alloc; // 分配器 private: // 内部使用函数 size_type alloc_capacity(size_type old_size) const // 容量分配函数 { //这个函数主要是为了方便修改分配方案， //可以按照需要修改，但是要确保返回值大于old_size，以此保证capacity()非空（看实现可知） // 提示：与c_str()的实现有关。 if(old_size < 10) return 10; //wstring else if(old_size < 100) return old_size * 2; else if(old_size < 1024) return old_size + old_size / 10; else return old_size + rand() % 1024 + 1; //返回值得大于old_size } void fill_n(pointer first,size_type n,value_type val) { assert(first != 0); while(n--) *first++ = val; } void fill(pointer first,pointer last,value_type val) { assert(first != 0 && last != 0); while(first != last) *first++ = val; } iterator insert_aux(size_type pos,const self& str) { //用于insert相关函数 assert(pos <= size()); if(str.empty()) return iterator(start+pos); if(size()+str.size() > capacity()) // 不管this是否等于&str { size_type str_size = str.size(); // size_type old_size = size(); size_type capacity_size = alloc_capacity(size()+str_size); pointer new_start = alloc.allocate(capacity_size); traits_type::copy(new_start,start,pos); traits_type::copy(new_start+pos,str.start,str_size); traits_type::copy(new_start+pos+str_size,start+pos,old_size-pos); alloc.deallocate(start,capacity()); start = new_start; finish = start + old_size+ + str_size; // end_of_storage = start + capacity_size; return iterator(start+pos); } else if(this != &str) { traits_type::move(start+pos+str.size(),start+pos,size()-pos); traits_type::copy(start+pos,str.start,str.size()); finish += str.size(); return iterator(start+pos); } else { size_type len_left = pos; size_type len_right = size() - pos; traits_type::copy(start+len_left*2+len_right,start+len_left,len_right); traits_type::copy(start+len_left,start,len_left); traits_type::copy(start+len_left*2,start+len_left*2+len_right,len_right); finish += str.size(); return iterator(start+len_left); } } iterator erase_aux(size_type first,size_type last) { //用于erase函数 assert(first <= last && last <= size()); if(first > size()) throw std::out_of_range("invalid string position"); if(first == last) return iterator(start+first); traits_type::copy(start+first,start+last,size()-last); finish -= last - first; return iterator(start+first); } void empty_init() { //用于初始化 size_type capacity_size = alloc_capacity(1); start = alloc.allocate(capacity_size); //分配一定的空间 finish = start; end_of_storage = start + capacity_size; } void swap(pointer& x,pointer& y) { assert(x != 0 && y != 0); pointer temp = x; x = y; y = temp; } bool is_inside(const self& str,value_type val) const { // 后面的查找功能的函数会用到，如find_first_of()函数 size_type n = str.size(); for(size_type i = 0; i < n; ++i) if(traits_type::eq(str[i],val)) return true; return false; } public: basic_string():start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t)); empty_init(); } basic_string(size_type n,value_type val):start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t)); size_type capacity_size = alloc_capacity(n); start = alloc.allocate(capacity_size); finish = start + n; end_of_storage = start + capacity_size; fill_n(start,n,val); } basic_string(const self& str,size_type pos,size_type len = npos) { assert(sizeof(value_type) <= sizeof(wchar_t)); assert(pos <= str.size()); if(str.empty()) empty_init(); else { if(len == npos || len > str.size()-pos) len = str.size() - pos; size_type capacity_size = alloc_capacity(len); start = alloc.allocate(capacity_size); traits_type::copy(start,str.start+pos,len); finish = start + len; end_of_storage = start + capacity_size; } } //这个构造函数不可用explicit关键字，后面大量用到此构造函数做隐式转换 basic_string(const_pointer str):start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t) && str != 0); size_type str_size = traits_type::length(str); size_type capacity_size = alloc_capacity(str_size); start = alloc.allocate(capacity_size); traits_type::copy(start,str,str_size); finish = start + str_size; end_of_storage = start + capacity_size; } basic_string(const_pointer str,size_type n):start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t) && str != 0); size_type len = traits_type::length(str); //标准库没有对长度进行调整(测试vs2012的运行结果可知),本人觉得应该加上，这样有更好的容错性 //当然，在str很大的时候，效率上会有点折扣（计算长度的时间花销上） if(n > len) n = len; size_type capacity_size = alloc_capacity(n); start = alloc.allocate(capacity_size); traits_type::copy(start,str,n); finish = start + n; end_of_storage = start + capacity_size; } template <class InputIterator> basic_string(InputIterator first,InputIterator last):start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t)); size_type len = 0; InputIterator new_first = first; while(new_first != last) //用后自增测试时会出现一点问题 ++len, ++new_first; size_type capacity_size = alloc_capacity(len); start = alloc.allocate(capacity_size); finish = start + len; /*while(first != last) *start++ = *first++;*/ while(last != first) //用后自增测试时会出现一点问题 *--finish = *--last; finish = start + len; // 复位 end_of_storage = start + capacity_size; } basic_string(const self& tmp):start(0),finish(0),end_of_storage(0) { assert(sizeof(value_type) <= sizeof(wchar_t)); start = alloc.allocate(tmp.capacity()); finish = start + tmp.size(); end_of_storage = start + tmp.capacity(); traits_type::copy(start,tmp.start,tmp.size()); } self& operator = (const self& tmp) { if(this == &tmp) // 防止自身复制 return *this; clear(); if(tmp.empty()) return *this; if(capacity() >= tmp.capacity()) { traits_type::copy(start,tmp.start,tmp.size()); finish = start + tmp.size(); } else { size_type capacity_size = alloc_capacity(tmp.size()); alloc.deallocate(start,capacity()); // 释放原有空间 start = alloc.allocate(capacity_size); traits_type::copy(start,tmp.start,tmp.size()); finish = start + tmp.size(); end_of_storage = start + capacity_size; } return *this; } self& operator = (value_type val) { clear(); // 不释放内存,看代码可知 insert_aux(0,self(1,val)); return *this; } ~basic_string() { //alloc.deallocate(start,capacity()); //由于capacity()实现上的缘故，这里用end_of_storage - start（看capacity代码可知） //当然，第二个参数事实上没有用，任意写一个数字都可 alloc.deallocate(start,end_of_storage - start); } public: size_type size() const throw() { //按照标准文档的要求，不抛出异常,以下同理可得,不再赘述！ return finish - start; } size_type length() const throw() { return size(); } size_type max_size() const throw() { return size_type(-1) / sizeof(value_type) - 1; } size_type capacity() const throw() { //这里的计算本来不应该减 1 的，有意这样做是为了确保留有一个字符的空间(包括宽字符）,方便做 // C风格字符串的转换,写入空字符，用于成员函数c_str() return end_of_storage - start - 1; } bool empty() const throw() { return start == finish; } iterator begin() throw() { return iterator(start); } const_iterator begin() const throw() { return const_iterator(start); } iterator end() throw() { return iterator(finish); } const_iterator end() const throw() { return const_iterator(finish); } reverse_iterator rbegin() throw() { return reverse_iterator(end()); } const_reverse_iterator rbegin() const throw() { return const_reverse_iterator(end()); } reverse_iterator rend() throw() { return reverse_iterator(begin()); } const_reverse_iterator rend() const throw() { return const_reverse_iterator(begin()); } reference operator [] (size_type n) throw() { assert(n < size()); return *(start + n); } const_reference operator [] (size_type n) const throw() { assert(n < size()); return *(start + n); } reference at(size_type n) { if(n < size()) return *(start + n); else throw std::out_of_range("invalid string position"); } const_reference at(size_type n) const { if(n < size()) return *(start + n); else throw std::out_of_range("invalid string position"); } allocator_type get_allocator() const throw() { return allocator_type(); } void reserve(size_type n = 0) { if(n <= capacity()) ; else { size_type capacity_size = alloc_capacity(n); size_type old_size = size(); pointer new_start = alloc.allocate(capacity_size); traits_type::copy(new_start,start,size()); alloc.deallocate(start,capacity()); start = new_start; finish = start + old_size; end_of_storage = start + capacity_size; } } void clear() { finish = start; //并不释放内存 } self substr(size_type pos = 0,size_type len = npos) const { assert(pos <= size()); return self(*this,pos,len); // 显式调用构造函数 } self& insert(size_type pos,const self& str) { assert(pos <= size()); insert_aux(pos,str); return *this; } const_pointer c_str() const throw() { //构造函数保证capacity() != 0,或者说start,finish,end_of_storage不为空指针 //当然，这和具体的实现有关，这是我的一个实现 *finish = 0; // 转换成C风格的字符串 return start; } const_pointer data() const throw() { *finish = 0; // 也可以直接返回start,标准文档没有强制要求为C风格字符串 return start; } self& insert(size_type pos,const self& str,size_type subpos,size_type sublen) { assert(pos <= size()); insert_aux(pos,str.substr(subpos,sublen)); return *this; } self& insert(size_type pos,const_pointer str) { assert(pos <= size() && str != 0); insert_aux(pos,self(str)); return *this; } self& insert(size_type pos,const_pointer str,size_type n) { assert(pos <= size() && str != 0); insert_aux(pos,self(str,n)); return *this; } self& insert(size_type pos,size_type n,value_type val) { assert(pos <= size()); insert_aux(pos,self(n,val)); return *this; } void insert(iterator itr,size_type n,value_type val) { assert(itr >= begin() && itr <= end()); insert_aux(itr-begin(),self(n,val)); } iterator insert(iterator itr,value_type val) { assert(itr >= begin() && itr <= end()); return insert_aux(itr-begin(),self(1,val)); } template <class InputIterator> void insert(iterator itr,InputIterator first,InputIterator last) { assert(itr >= begin() && itr <= end()); insert_aux(itr-begin(),self(first,last)); } self& erase(size_type pos = 0,size_type len = npos) { assert(pos <= size()); if(pos > size()) throw std::out_of_range("invalid string position"); if(len == npos || len > size()-pos) len = size() - pos; erase_aux(pos,pos+len); return *this; } iterator erase(iterator itr) { assert(itr >= begin() && itr < end()); return erase_aux(itr-begin(),itr-begin()+1); } iterator erase(iterator first,iterator last) { assert(first >= begin() && first <= last && last <= end()); return erase_aux(first-begin(),last-begin()); } void push_back(value_type val) { insert_aux(size(),self(1,val)); } self& append(const self& str) { return *this += str; } self& append(const self& str,size_type subpos,size_type sublen) { return *this += str.substr(subpos,sublen); } self& append(const_pointer str) { assert(str != 0); return *this += str; } self& append(const_pointer str,size_type n) { assert(str != 0); return *this += self(str,n); } self& append(size_type n,value_type val) { return *this += self(n,val); } template <class InputIterator> self& append(InputIterator first,InputIterator last) { return *this += self(first,last); } self& assign(const self& str) { return *this = str; } self& assign(const self& str,size_type subpos,size_type sublen) { return *this = self(str,subpos,sublen); } self& assign(const_pointer str) { assert(str != 0); return *this = self(str); } self& assign(const_pointer str,size_type n) { assert(str != 0); return *this = self(str,n); } self& assign(size_type n,value_type val) { return *this = self(n,val); } template <class InputIterator> self& assign(InputIterator first,InputIterator last) { return *this = self(first,last); } void resize(size_type n) { resize(n,0); //转调 } void resize(size_type n,value_type val) { if(n <= size()) finish -= size() - n; else if(n <= capacity()) { fill(finish,finish+n,val); finish += n - size(); } else { size_type capacity_size = alloc_capacity(n); pointer new_start = alloc.allocate(capacity_size); traits_type::copy(new_start,start,size()); fill(new_start+size(),new_start+n,val); alloc.deallocate(start,capacity()); start = new_start; finish = start + n; end_of_storage = start + capacity_size; } } void swap(self& str) { if(this == &str) return ; swap(start,str.start); swap(finish,str.finish); swap(end_of_storage,str.end_of_storage); } self& replace(size_type pos,size_type len,const self& str) { assert(pos <= size()); if(pos > size()) throw std::out_of_range("invalid string position"); // 后面的replace重载函数就不用写异常了，因为都会直接或间接地调用到这个函数 if(len > size() - pos) len = size() - pos; if(size() + str.size() - len > capacity()) { size_type new_size = size()+str.size()-len; size_type capacity_size = alloc_capacity(new_size); pointer new_start = alloc.allocate(capacity_size); traits_type::copy(new_start,start,pos); traits_type::copy(new_start+pos,str.start,str.size()); traits_type::copy(new_start+pos+str.size(),start+pos+len,size()-pos-len); alloc.deallocate(start,capacity()); start = new_start; finish = start + new_size; end_of_storage = start + capacity_size; } else if(this != &str) //如果不是自身的替换 { if(str.size() <= len) { traits_type::copy(start+pos,str.start,str.size()); erase(pos+str.size(),len-str.size()); // 长度len - str.size() // finish 已经更新 } else // size() + str.size() - len <= capacity() { traits_type::move(start+pos+str.size(),start+pos+len,size()-pos-len); traits_type::copy(start+pos,str.start,str.size()); finish += str.size() - len; } } else return replace(pos,len,self(str)); //递归调用，这次不会是自身了。 return *this; } self& replace(iterator itr_1,iterator itr_2,const self& str) { assert(itr_1 >= begin() && itr_2 <= end()); return replace(itr_1-begin(),itr_2-itr_1,str); // 转调 } self& replace(size_type pos,size_type len,const self& str, size_type subpos,size_type sublen) { assert(pos <= size()); return replace(pos,len,str.substr(subpos,sublen)); } self& replace(size_type pos,size_type len,const_pointer str) { assert(pos <= size() && str != 0); return replace(pos,len,self(str)); } self& replace(iterator itr_1,iterator itr_2,const_pointer str) { assert(itr_1 >= begin() && itr_2 <= end()); return replace(itr_1,itr_2,self(str)); //转调 } self& replace(size_type pos,size_type len,const_pointer str,size_type n) { assert(pos <= size() && str != 0); return replace(pos,len,self(str,n)); } self& replace(iterator itr_1,iterator itr_2,const_pointer str,size_type n) { assert(itr_1 >= begin() && itr_2 <= end() && str != 0); return replace(itr_1,itr_2,self(str,n)); } self& replace(size_type pos,size_type len,size_type n,value_type val) { assert(pos <= size()); return replace(pos,len,self(n,val)); } self& replace(iterator itr_1,iterator itr_2,size_type n,value_type val) { assert(itr_1 >= begin() && itr_2 <= end()); return replace(itr_1,itr_2,self(n,val)); } template <class InputIterator> self& replace(iterator itr_1,iterator itr_2,InputIterator first,InputIterator last) { assert(itr_1 >= begin() && itr_2 <= end()); return replace(itr_1,itr_2,self(first,last)); } int compare(const self& str) const { //后面的compare重载函数都间接调用此函数 if(this == &str) return 0; size_type num = size() >= str.size() ? size() : str.size(); return traits_type::compare(c_str(),str.c_str(),num); //需要转换为C风格字符串 } int compare(size_type pos,size_type len,const self& str) const { assert(pos <= size()); if(pos > size()) // 后面的重载函数不用写异常了，这里写了 throw std::out_of_range("invalid string position"); //size_type num = len >= str.size() ? len : str.size(); //return traits_type::compare(start+pos,str.start,num); return substr(pos,len).compare(str); //转调 } int compare(size_type pos,size_type len,const self& str, size_type subpos,size_type sublen) const { assert(pos <= size()); return compare(pos,len,self(str,subpos,sublen)); //转调 } int compare(const_pointer str) const { assert(str != 0); return compare(self(str)); } int compare(size_type pos,size_type len,const_pointer str) const { assert(pos <= size() && str != 0); return compare(pos,len,self(str)); } int compare(size_type pos,size_type len,const_pointer str,size_type n) const { assert(pos <= size() && str != 0); return compare(pos,len,self(str,n)); } size_type copy(pointer str,size_type len,size_type pos = 0) const { assert(pos <= size() && str != 0); if(len + pos > size()) len = size() - pos; // 调整一下长度 traits_type::copy(str,start+pos,len); return len; } size_type find(const self& str,size_type pos = 0) const throw() { //pos为搜索开始处，用数学区间表示为[pos,size() ) assert(pos <= size()); if(empty()) return npos; size_type len_str = str.size(); size_type len = size() - pos; if(len < len_str) return npos; size_type end_pos = size() - len_str; // 调整了一下有效长度，避免做无用功 while(pos <= end_pos) { if(compare(pos,len_str,str) == 0) // 转调重载的成员函数 return pos; else ++pos; } return npos; } size_type find(const_pointer str,size_type pos = 0) const throw() { assert(pos <= size() && str != 0); if(empty()) return npos; return find(self(str),pos); // 转调重载的成员函数 } size_type find(const_pointer str,size_type pos,size_type n) const throw() { //str中的n个字符,注意 n 的具体所指 assert(pos <= size() && str != 0); if(empty()) return npos; return find(self(str,n),pos);// 转调重载的成员函数 } size_type find(value_type val,size_type pos = 0) const throw() { assert(pos <= size()); if(empty()) return npos; return find(self(1,val),pos); // 转调重载的成员函数 } size_type rfind(const self& str,size_type pos = npos) const throw() { // pos为搜索开始处，用数学区间表示为[0,pos] if(empty()) return npos; if(pos == npos || pos >= size()) //加上pos == npos的判断并非多此一举 pos = size() - 1; if(size() < str.size()) return npos; size_type len_str = str.size(); if(pos > size() - len_str) pos = size() - len_str; // 调整位置，避免做无用的搜索 while(pos >= 0 && pos != size_type(-1)) { if(compare(pos,len_str,str) == 0) // 转调成员函数 return pos; else --pos; } return npos; } size_type rfind(const_pointer str,size_type pos = npos) const throw() { assert(str != 0); if(empty()) return npos; if(pos == npos || pos >= size()) //加上pos == npos的判断并非多此一举 pos = size() - 1; return rfind(self(str),pos); // 转调重载的成员函数 } size_type rfind(const_pointer str,size_type pos,size_type n) const throw() { // n为str需要搜索字符的个数,因为构造函数实现上的差异，我的n值在调用构造函数时会有调整， // 这样是为了增强容错性，但是测试vs2012可知此实现上没有此功能， //因此，用标准库时，依赖于用户使用正确的n值，否则会得不到预期的结果， // 用我的这个实现，当n值大于str的长度时，会匹配整个str字符串 //类似情况同理可知，不再赘述。 assert(str != 0); if(empty()) return npos; if(pos >= size()) pos = size() - 1; return rfind(self(str,n),pos); // 转调重载的成员函数 } size_type rfind(value_type val,size_type pos = npos) const throw() { if(empty()) return npos; if(pos == npos || pos >= size()) pos = size() - 1; return rfind(self(1,val),pos); // 转调重载的成员函数 } size_type find_first_of(const self& str,size_type pos = 0) const throw() { //pos为搜索开始处，用数学区间表示为[pos,size() ) assert(pos <= size()); if(empty()) return npos; size_type end_pos = size(); while(pos != end_pos && !is_inside(str,*(start+pos))) ++pos; if(pos == end_pos) return npos; else return pos; } size_type find_first_of(const_pointer str,size_type pos = 0) const throw() { //pos为搜索开始处，范围为[pos,size() ) assert(pos <= size() && str != 0); if(empty()) return npos; return find_first_of(self(str),pos); // 转调重载的成员函数 } size_type find_first_of(const_pointer str,size_type pos, size_type n) const throw() { //pos为搜索开始处，范围为[pos,size() ) assert(pos <= size() && str != 0); if(empty()) return npos; return find_first_of(self(str,n),pos); // // 转调重载的成员函数 } size_type find_first_of(value_type val,size_type pos = 0) const throw() { //pos为搜索开始处，范围为[pos,size() ) assert(pos <= size()); if(empty()) return npos; return find_first_of(self(1,val),pos); // 转调重载的成员函数 } size_type find_last_of(const self& str,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos],包含pos if(empty()) return npos; if(pos == npos || pos >= size()) //加上pos == npos的判断并非多此一举 pos = size() - 1; while(pos >= 0 && pos != size_type(-1) && !is_inside(str,*(start+pos))) --pos; if(pos != size_type(-1)) return pos; else return npos; } size_type find_last_of(const_pointer str,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos],包含pos if(empty()) return npos; assert(str != 0); if(pos == npos || pos >= size()) pos = size() - 1; return find_last_of(self(str),pos); // 转调重载的成员函数 } size_type find_last_of(const_pointer str,size_type pos,size_type n) const throw() { //pos 搜索结束处，范围[0,pos],包含pos assert(str != 0); if(empty()) return npos; if(pos >= size()) pos = size() - 1; return find_last_of(self(str,n),pos); // 转调重载的成员函数 } size_type find_last_of(value_type val,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos],包含pos if(empty()) return npos; if(pos == npos || pos >= size()) pos = size() - 1; return find_last_of(self(1,val),pos); // 转调重载的成员函数 } size_type find_first_not_of(const self& str,size_type pos = 0) const throw() { //pos 为搜索开始处，范围[pos,size() ) assert(pos <= size()); if(empty()) return npos; size_type end_pos = size(); while(pos != end_pos && is_inside(str,*(start+pos))) ++pos; if(pos == end_pos) return npos; else return pos; } size_type find_first_not_of(const_pointer str,size_type pos = 0) const throw() { //pos 为搜索开始处，范围[pos,size() ) assert(pos <= size() && str != 0); if(empty()) return npos; return find_first_not_of(self(str),pos); } size_type find_first_not_of(const_pointer str,size_type pos,size_type n) const throw() { //pos 为搜索开始处，范围[pos,size() ) assert(pos <= size() && str != 0); if(empty()) return npos; return find_first_not_of(self(str,n),pos); // 转调重载的成员函数 } size_type find_first_not_of(value_type val,size_type pos = 0) const throw() { //pos 为搜索开始处，范围[pos,size() ) assert(pos <= size()); if(empty()) return npos; return find_first_not_of(self(1,val),pos); } size_type find_last_not_of(const self& str,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos] if(empty()) return npos; if(pos == npos || pos >= size()) pos = size() - 1; while(pos >= 0 && pos != size_type(-1) && is_inside(str,*(start+pos))) --pos; if(pos != size_type(-1)) return pos; else return npos; } size_type find_last_not_of (const_pointer str,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos] assert(str != 0); if(empty()) return npos; if(pos == npos || pos >= size()) //加上pos == npos的判断并非多此一举 pos = size() - 1; return find_last_not_of(self(str),pos); // 转调重载的成员函数 } size_type find_last_not_of (const_pointer str,size_type pos,size_type n) const throw() { //pos 搜索结束处，范围[0,pos] assert(str != 0); if(empty()) return npos; if(pos >= size()) pos = size() - 1; return find_last_not_of(self(str,n),pos); // 转调重载的成员函数 } size_type find_last_not_of (value_type val,size_type pos = npos) const throw() { //pos 搜索结束处，范围[0,pos] if(empty()) return npos; if(pos == npos || pos >= size()) pos = size() - 1; return find_last_not_of(self(1,val),pos); // 转调重载的成员函数 } self& operator += (const self& str) { insert_aux(size(),str); return *this; } self& operator += (value_type val) { insert_aux(size(),self(1,val)); return *this; } friend self operator + (const self& str1,const self& str2) { return self(str1) += str2; } friend self operator + (const self& str,value_type val) { return self(str) += self(1,val); } friend self operator + (value_type val,const self& str) { return self(1,val) += str; } friend void swap(self& str1,self& str2) { if(&str1 == &str2) return ; str1.swap(str2); } friend bool operator == (const self& str1,const self& str2) { return str1.compare(str2) == 0; } friend bool operator != (const self& str1,const self& str2) { return str1.compare(str2) != 0; } friend bool operator < (const self& str1,const self& str2) { return str1.compare(str2) < 0; } friend bool operator <= (const self& str1,const self& str2) { return str1.compare(str2) <= 0; } friend bool operator > (const self& str1,const self& str2) { return str1.compare(str2) > 0; } friend bool operator >= (const self& str1,const self& str2) { return str1.compare(str2) >= 0; } }; template <class charT, class traits, class Alloc> std::basic_istream<charT,traits>& operator >> (std::basic_istream<charT,traits>& is, mystd::basic_string<charT,traits,Alloc>& str) { str.clear(); //先清空str int chr = 0; //对wchar_t类型字符也适用 while((chr = is.get()) && chr != ' ' && chr != '\n') str.push_back(chr); return is; } template <class charT, class traits, class Alloc> std::basic_ostream<charT,traits>& operator<< (std::basic_ostream<charT,traits>& os, const mystd::basic_string<charT,traits,Alloc>& str) { typedef typename mystd::basic_string<charT,traits,Alloc>::size_type size_type; size_type size = str.size(); for(size_type i = 0; i < size; ++i) os<<str[i]; return os; } template <class charT, class traits, class Alloc> std::basic_istream<charT,traits>& getline(std::basic_istream<charT,traits>& is, mystd::basic_string<charT,traits,Alloc>& str, charT delim) { charT chr = 0; str.clear(); //先清空str while((chr = is.get()) && chr != delim && chr != '\n') str.push_back(chr); return is; } template <class charT, class traits, class Alloc> std::basic_istream<charT,traits>& getline(std::basic_istream<charT,traits>& is, mystd::basic_string<charT,traits,Alloc>& str) { charT chr = 0; str.clear(); //先清空str while((chr = is.get()) && chr != '\n') str.push_back(chr); return is; } typedef mystd::basic_string<char,std::char_traits<char>,std::allocator<char> > string; typedef mystd::basic_string<wchar_t,std::char_traits<wchar_t>,std::allocator<wchar_t> > wstring; MYSTD_END // end of namespace mystd #endif // __cplusplus #endif // MYSTD_STRING_H_EX最后加一个我在公司项目中经常使用的两个函数：
#include <string> #include <iostream> using namespace std; string& replace_all(string& str,const string& old_value,const string& new_value) { while(true) { string::size_type pos(0); if( (pos=str.find(old_value))!=string::npos ) str.replace(pos,old_value.length(),new_value); else break; } return str; } string& replace_all_distinct(string& str,const string& old_value,const string& new_value) { for(string::size_type pos(0); pos!=string::npos; pos+=new_value.length()) { if( (pos=str.find(old_value,pos))!=string::npos ) str.replace(pos,old_value.length(),new_value); else break; } return str; } int main() { cout << replace_all(string("12212"),"12","21") << endl; cout << replace_all_distinct(string("12212"),"12","21") << endl; } /* 输出如下: */