解读STL的string类中各方法的使用场景

2024-12-11 技术教程

所在头文件：<string>

实现：typedf basic_string<char> string

所在命名空间：std

功能：标准string提供字节标准容器的接口，同事增加对字符串中单独的字符的操作。由于标准string是basic_string<char>的一种特化，只能针对char型，如果字符编码方式是多字节或者可变字符序列（eg：UTF-8）那么它仍然按字节去解读，而不是按照传入内容的编码方式。

（1）成员函数number functions

constructor（构造函数）创建string对象 (公有成员函数)
destructor （析构函数）销毁string对象（公有成员函数）operator= （赋值运算符重载）

将一个string对象赋给另一个string对象

（公有成员函数）

（2）Iterators

beginiterator begin();
const_iterator begin() const;
返回一个迭代器指向string对象的第一个字符enditerator end() noexcept;

const_iterator end() const noexcept;

（noexcept是c11对异常的处理方式）

返回一个迭代器指向string对象的结束字符的位置（‘\0’处），不可引用

如果是空串end=begin

rbeginreverse_iterator rbegin() noexcept;
const_reverse_iterator rbegin() const noexcept;

返回一个反向迭代器指向string对象的结束字符的位置

反向迭代器向后遍历-->向begin走

rendreverse_iterator rend() noexcept;
const_reverse_iterator rend() const noexcept;

返回一个反向迭代器指向string对象的第一个字符的位置

cbeginconst_iterator cbegin() const noexcept;
返回一个const迭代器指向string对象的第一个字符的位置cendconst_iterator cend() const noexcept;
返回一个const迭代器指向string对象的结束字符的位置crbeginconst_reverse_iterator crbegin() const noexcept;
返回一个const反向迭代器指向string对象的结束字符的位置crendconst_reverse_iterator crend() const noexcept;
返回一个const反向迭代器指向string对象的第一个字符的位置

例子：

//string::begin/end#include<iostream>#include<string>usingnamespacestd:voidtest1(){stringstr("Teststring");for(string::iteratorit=str.begin();it!=str.end();++it){cout<<*it;}cout<<endl;}//string::rbegin/rendvoidtest2(){stringstr("nowsteplive...");for(string::reverse_iteratorrit=str.rbegin();rit!=str.rend();++rit)cout<<*rit;}//string::cbegin/cendvoidtest3(){stringstr("Loremipsum");for(autoit=str.cbegin();it!=str.cend();++it)cout<<*it;cout<<endl;}//string::crbegin/crendvoidtest4(){stringstr("loremipsum");for(autorit=str.crbegin();rit!=str.crend();++rit)cout<<*rit;cout<<endl;}intmain(){test1();test2();test3();test4();return0;}

(3)Capacity

size
size_t size() const noexcept;

返回string的字节个数（size_t类型）

size！=capacity

lengthsize_t length() const noexcept;

返回string的字节个数（size_t类型）

length！=capacity

max_sizesize_t max_size() const noexcept;

返回string可以达到的最大长度

（极限范围，可能按max_size内存分配失败）

max_size!=capacity

resize
void resize (size_t n);
void resize (size_t n, char c);

重置string的长度，设置为n

重置string的长度，设置为n，内容用c填充

如果n<string的原length，超过n部分舍弃

如果n>string的原length,先拷贝原先的在加上

c的部分（没有c，就是空字符）

capacity
size_t capacity() const noexcept;
返回已分配给string的内存的字节个数reversevoid reserve (size_t n = 0);

改变string的capacity为n

不改变length和内容

clearvoid clear() noexcept;

清除string的内容，让string变成一个空串

length=0

emptybool empty() const noexcept;

返回string是否为空，为空返回true，非空返回

false

shrink_to_fitvoid shrink_to_fit();
减小string的capacity到size大小

例子：

#include<iostream>#include<string>usingnamespacestd;//comparingsize,length,capacityandmax_sizevoidtest1(){stringstr("Teststring");cout<<"size:"<<str.size()<<endl;cout<<"length:"<<str.length()<<endl;cout<<"capacity:"<<str.capacity()<<endl;cout<<"max_size:"<<str.max_size()<<endl;}//string::shrink_to_fitvoidtest2(){stringstr("IliketocodeinC");cout<<str<<endl;unsignedsz=str.size();str.resize(sz+2,'+');cout<<str<<endl;str.resize(14);cout<<str<<endl;}//string::shrink_to_fitvoidtest3(){stringstr(100,'x');cout<<"1.capacityofstr:"<<str.capacity()<<endl;str.resize(10);cout<<"2.capacityofstr:"<<str.capacity()<<endl;str.shrink_to_fit();cout<<"3.capacityofstr:"<<str.capacity()<<endl;}

(4)Element access

operator[]
char& operator[] (size_t pos);
const char& operator[] (size_t pos) const;
返回string[pos]的字符at char& at (size_t pos);
const char& at (size_t pos) const;
返回string[pop]的字符前会检查pos是不是字符范围内，超出范围会抛异常backchar& back();
const char& back() const;
返回最后一个字符的引用frontchar& front();
const char& front() const;
返回第一个字符的引用

例子：

#include<iostream>#include<string>usingnamespacestd;//string::operator[]voidtest1(){stringstr("Teststring");for(inti=0;i<str.length();++i){cout<<str[i];}}//string::atvoidtest2(){stringstr("Teststring");for(inti=0;i<str.size();i++){cout<<str.at(i);}}//string::backvoidtest3(){stringstr("helloworld.");str.back()='!';cout<<str<<endl;}//string::frontvoidtest4(){stringstr("teststring");str.front()='T';cout<<str<<endl;}

(5)Modifiers

operator+=

string& operator+= (const string& str);

string& operator+= (const char* s);

string& operator+= (char n);

string& operator+= (initializer_list<char> il);

在现有的string后面添加字符串/字符append

string& append (const string& str);

string& append (const string& str, size_t subpos, size_t sublen);

string& append (const char* s);

string& append (const char* s, size_t n);

string& append (size_t n, char c);

template <class InputIterator>
string& append (InputIterator first, InputIterator last);

string& append (initializer_list<char> il);

在现有的string后面添加字符串/字符push_back
void push_back(char c);
将字符c添加在string末尾，length++assign

string& assign(const string& str);

string& assign(const string& str, size_t subpos, size_t sublen);

string& assign(const char * s);

string& assign(const char *s,size_t n);

string &assign(size_t n,char c);

template<class InputIterator>

string& assign(InputIterator first,InputIterator last);

string& assign(initializer_list<char> il);

将现有的字符串string替换成新的字符串insert

string & insert (size_t pos,const string & str );

string & insert (size_t pos,const string & str,size_t subpos,size_t sublen);

string & insert(size_t pos,const char *s);

string & insert(size_t pos,const char *s,size_t n);

string & insert(size_t pos,size_t n,char c);

void insert (iterator p, size_t n, char c);

iterator insert (iterator p, char c);

template <class InputIterator>
void insert (iterator p, InputIterator first, InputIterator last);

将现有字符串string的pos位置后面插入字符串或者字符erase

string & erase(size_t pos=o,size_t len=pos);

iterator erase(iterator p);

iterator erase(iterator first,iterator last);

将现有字符串删除一部分，length也有减少replace

string & repalce(size_t pos,size_t len,const string& str);

string & repalce(iterator i1,iterator i2,const string &str);

string & repalce (size_t pos,size_t len,const string & str,size_t subpos,size_t sublen);

string & replace(size_t pos,size_t len,const char *s);

string & replace(iterator i1,iterator i2,const char *s);

string & repalce(size_t pos,size_t len,const char*s,size_t n);

string & repalce(iterator i1,iterator i2,const char*s,size_t n);

string & raplace(size_t pos,size_t len,size_t n,char c);

string & repalce(iterator i1,iterator i2,size_t n,chr c);

template <class InputIterator>

string & repalce(iterator i1, iterator i2,InputIterator first,InputIterator last);

将现有字符串的一部分用新的字符串或者字符序列，字符去替换swapvoid swap(string & str);
两个字符串的内容进行交换pop_back

void pop_back();

将字符串末尾的字符删除

例子：

#include<iostream>#include<string>usingnamespacestd;//string::operator+=voidtest1(){stringname("John");stringfamily("Smith");name+="K.";//c-stringname+=family;//stringname+='\n';//charactercout<<name;}//string::appendvoidtest2(){stringstr;stringstr2="Writing";stringstr3="print10andthen5more";//string&append(conststring&str);str.append(str2);//Writing//string&append(conststring&str,size_tpos,size_tlength);str.append(str3,6,3);//Writing10//string&append(constchar*s,size_tn);str.append("dotsarecool",5);//Writing10dots//string&append(constchar*s);str.append("here:");//Writing10dotshere://string&append(size_tn,charc);str.append(10u,'.');//Writing10dotshere:..........//strin&append(inputIteratorfirst,inputIteratorlast);str.append(str3.begin()+8,str3.end());//Writing10dotshere:.........andthen5more//string&append(size_tn,)str.append<int>(5,0x2E);//Writing10dotshere:.........andthen5more.....cout<<str<<endl;}//string::assignvoidtest3(){stringstr;stringstr1=“helloworld”;str.assign(str1);cout<<str<<endl;str.assign(str1,7,5);cout<<str<<endl;str.assign("abcedf");cout<<str<<endl;str.assign("abcdrf",5);cout<<str<<endl;str.assign(5u,'.');cout<<str<<endl;cout<<assign(str1.begin()+6,str1.end());cout<<str<<endl;str.assign<int>(10,0x2D);cout<<str<<endl;}//string::insertvoidtest4(){stringstr="tobequestion";stringstr2="the";stringstr3="ornottobe";string::iteratorit;//usedinthesameorderasdescribedabove:str.insert(6,str2);//tobe(the)questionstr.insert(6,str3,3,4);//tobe(not)thequestionstr.insert(10,"thatiscool",8);//tobenot(thatis)thequestionstr.insert(10,"tobe");//tobenot(tobe)thatisthequestionstr.insert(15,1,':');//tobenottobe(:)thatisthequestionit=str.insert(str.begin()+5,',');//tobe(,)nottobe:thatisthequestionstr.insert(str.end(),3,'.');//tobe,nottobe:thatisthequestion(...)str.insert(it+2,str3.begin(),str3.begin()+3);//(or)cout<<str<<endl;}//string::erasevoidtest5(){stringstr("Thisisanexamplesentence.");cout<<str<<endl;//"Thisisanexamplesentence."str.erase(10,8);cout<<str<<endl;;//"Thisisansentence."str.erase(str.begin()+9);cout<<str<<endl;;//"Thisisasentence."str.erase(str.begin()+5,str.end()-9);std::cout<<str<<endl;;//"Thissentence."}//string::repalcevoidtest6(){stringbase="thisisateststring.";stringstr2="nexample";stringstr3="samplephrase";stringstr4="useful.";//replacesignaturesusedinthesameorderasdescribedabove://Usingpositions:stringstr=base;//"thisisateststring."str.replace(9,5,str2);//"thisisanexamplestring."(1)str.replace(19,6,str3,7,6);//"thisisanexamplephrase."(2)str.replace(8,10,"justa");//"thisisjustaphrase."(3)str.replace(8,6,"ashorty",7);//"thisisashortphrase."(4)str.replace(22,1,3,'!');//"thisisashortphrase!!!"(5)//Usingiterators:str.replace(str.begin(),str.end()-3,str3);//"samplephrase!!!"(1)str.replace(str.begin(),str.begin()+6,"replace");//"replacephrase!!!"(3)str.replace(str.begin()+8,str.begin()+14,"iscoolness",7);//"replaceiscool!!!"(4)str.replace(str.begin()+12,str.end()-4,4,'o');//"replaceiscooool!!!"(5)str.replace(str.begin()+11,str.end(),str4.begin(),str4.end());//"replaceisuseful."(6)std::cout<<str<<endl;}//string::swapvoidtest7(){stringbuyer("money");stringseller("goods");cout<<"Beforetheswap,buyerhas"<<buyer;cout<<"andsellerhas"<<seller<<endl;seller.swap(buyer);cout<<"Aftertheswap,buyerhas"<<buyer;cout<<"andsellerhas"<<seller<<endl;}//string::pop_backvoidtest8(){stringstr("helloworld!");str.pop_back();cout<<str<<endl;}

(6)String operations

c_strconst char * c_str()const;
返回一个const char *型的指针，内容是string的内容+‘\0’dataconst char * data()const;返回一个const char *型的指针，即得到string对象的c_string形式

get_allocator

allocator_type get_allocator()const;返回一个allocator——type型的string的拷贝copy
size_t copy(char*s,size_t len,size_t pos=0)const;

拷贝一个string中的子串到s所指的数组

（拷贝版不会自己添加'\0'）

find

size_t find(cosnt string &str,size_t pos=0)const;

size_t find(const char *s,size_t pos=0)const;

size_t find(const char *s,size_t pos,size_t n)const;

size_t find(char c,size_t pos=0)const;

查找所找字符串序列第一次出现的位置substr

string substr(size_t pos=0,size_t len=npos)const;

返回子串compare

int compare(const string& str)const;

int compare(size_t pos,size_t len,const string &str)const;

int compare(size_t pos,size_t len,const string &str,size_t subpos,size_t

sublen)const;

int compare(const char* s)const;

int compare(size_t pos,size_t len,const char *s)const;

int compare(size_t pos,size_tlen,const char *s,size_t n)const;

比较两个字符串

例子：

#include<iostream>#include<string>usingnamespacestd;//string::c_str()voidtest1(){stringstr("Pleasesplitthissentenceintotokens");char*cstr=newchar[str.length()+1];strcpy(cstr,str.c_str());//cstrnowcontainsac-stringcopyofstrchar*p=strtok(cstr,"");//线程不安全的字符串分割函数while(p!=0){cout<<p<<endl;//依次输出Pleasesplit直到NULLp=strtok(NULL,"");}delete[]cstr;}//string::data()voidtest2(){intlength;stringstr="Teststring";char*cstr="Teststring";if(str.length()==std::strlen(cstr)){cout<<"strandcstrhavethesamelength."<<endl;if(memcmp(cstr,str.data(),str.length())==0)cout<<"strandcstrhavethesamecontent."<<endl;}}//string::copyvoidtest3(){charbuffer[20];stringstr("Teststring...");size_tlength=str.copy(buffer,6,5);buffer[length]='\0';cout<<"buffercontains:"<<buffer<<endl;}//string::comparevoidtest4(){stringstr1("greenapple");stringstr2("redapple");if(str1.compare(str2)!=0)cout<<str1<<"isnot"<<str2<<endl;if(str1.compare(6,5,"apple")==0)cout<<"still,"<<str1<<"isanapple"<<endl;if(str2.compare(str2.size()-5,5,"apple")==0)cout<<"and"<<str2<<"isalsoanapple"<<endl;if(str1.compare(6,5,str2,4,5)==0)cout<<"therefore,bothareapples"<<endl;}

（7）成员常量

npos

size_t的最大范围

static const int npos=-1;

(定义时就初始化)

（8）非成员函数的重载

operator+串联字符串relational operator

各种运算符的重载

swap

交换两个字符串，std所属函数，非string所属

operator>>

输入一个字符串