string类专题
string是一个类，它有很多成员方法，我们平时开发也主要是关注string在字符串处理方面的用法。所以本文主要以代码案例来说明其用法。以下案例涵盖了string类的绝大数多数成员方法的使用，开发时可作为手册快速查询。（代码经过全面自测可直接使用）
#include <iostream>
#include <string>
#include <cstring> //比如要使用strcpy
#include <cstddef> //std::size_t
#include <fstream>
using namespace std;
void SplitFilename(const string &str){
cout<<"Splitting: "<<str<<'\n';
size_t found = str.find_last_of("/\\");
cout<<" path: "<<str.substr(0, found)<<'\n'; //目录
cout<<" file: "<<str.substr(found+1)<<'\n'; //文件名或最内层文件夹名
}
int main()
{
//string的初始化
string string_1("string 1");
string string_2;
string_2 = "string 2";
//从标准输入读取一整行
string string_3;
getline(cin, string_3, '\n');
//字符串还可以拼接
string string_4 = string_1 + string_2 + string_3;
cout<<string_4<<endl;
string string_5;
string_5 += "hello string 5";
cout<<string_5<<endl;
//字符串的比较
string string_6;
getline(cin, string_6, '\n');
if(string_6 == "xyz"){
cout<<"Access allowed"<<endl;
}
//求字符串的长度
string string_7 = "my name is string 7";
int len = string_7.length(); //or .size()
cout<<len<<endl; //19
//访问字符串的单个元素,就像访问数组一样
for(int i = 0;i < string_7.size();i++){
cout<<string_7[i]<<endl;
}
//使用string类型的迭代器访问字符串的单个元素
string::iterator iter;
for(iter = string_7.begin(); iter != string_7.end();++iter){
cout<<*iter<<endl;
}
//string类支持简单的查询和截取
string string_8;
getline(cin, string_8, '\n');
int cat_find = 0;
for(int i = string_8.find("cat", 0);i != string_8.npos;i = string_8.find("cat", i)){//string::npos, that indicates that it did not find the substring
cat_find++;
i++;
}
cout<<cat_find<<endl;
string string_9 = "abcdefghijklabcdilj";
string sub_string_9 = string_9.substr(1, 5);
cout<<sub_string_9<<endl; //bcdef
//string的修改
string string_A = "12345678";
string_A.erase(3, 2); //从位置3(包含位置3)往后去除2个元素
cout<<string_A<<endl; //123678
//删除整个字符串
string string_B = "1232ljfasf";
string_B.erase(0, string_B.length());
//插入字符串到一个已经存在的字符串中
string string_C = "abef";
string_C.insert(2, "cd");
cout<<string_C<<endl; //abcdef
//string类的成员方法用例
//append 方法: Extends the string by appending additional characters at the end of its current value
string str;
string str2 = "Writing ";
string str3 = "print 10 and then 5 more";
str.append(str2); //"Writing "
str.append(str3, 6, 3); //"10 " 从str3的第6个位置截取3个字符
str.append("dots are cool", 5); //"dots " //默认从位置 0 开始截取5个字符
str.append("here: "); //"here: "
str.append(10u,'.'); //".........."
str.append(str3.begin()+8, str3.end()); //" and then 5 more"
//str.append<int>(5, 0x2E);
cout<<str<<endl; //Writing 10 dots here: .......... and then 5 more
//assign 方法: Assigns a new value to the string, replacing its current contents
string str_A;
string base = "The quick brown fox jumps over a lazy dog.";
str_A.assign(base); //"The quick brown fox jumps over a lazy dog."
cout<<str_A<<endl;
str_A.assign(base, 10, 9);
cout<<str_A<<endl; //"brown fox"
str_A.assign("pangrams are cool", 7);
cout<<str_A<<endl; //"pangram"
str_A.assign("c-string");
cout<<str_A<<endl; //"c-string"
str_A.assign(10, '*');
cout<<str_A<<endl; //"**********"
str_A.assign(base.begin()+16, base.end()-12); //从位置16到倒数12位置结束的这段
cout<<str_A<<endl; //"fox jumps over"
//at 方法:Returns a reference to the character at position pos in the string
string str_B("Test string");
for(unsigned i = 0;i < str_B.length(); ++i){
cout<<str_B.at(i);
}
//back 方法:Returns a reference to the last character of the string
string str_C("hello world");
str_C.back() = '!'; //替换原始字符串中的最后一个字符
cout<<str_C<<endl; //"hello worl!"
//begin 方法:Returns an iterator pointing to the first character of the string.
for(string::iterator iter = str_C.begin(); iter != str_C.end();++iter){
cout<<*iter<<endl;
}
//capacity 方法:Returns the size of the storage space currently allocated for the string
//This capacity is not necessarily equal to the string length. It can be equal or greater, with the extra space allowing the object to optimize its operations when new characters are added to the string
//The capacity of a string can be explicitly altered by calling member reserve
cout<<"size: "<<str_C.size()<<endl; //11
cout<<"length: "<<str_C.length()<<endl; //11
cout<<"capacity: "<<str_C.capacity()<<endl; //15
cout<<"max_size: "<<str_C.max_size()<<endl; //9223372036854775807
//cbegin, cend 方法:它跟 begin 方法类似都是返回一个 iterator.只是这个方法无条件返回 const_iterator
string str_D("Lorem ipsum");
for(auto it = str_D.cbegin();it != str_D.cend();++it){
cout<<*it<<endl;
}
//clear 方法:Erases the contents of the string, which becomes an empty string (with a length of 0 characters).
char c;
string str_E;
cout<<"Please type some lines of text.Enter a dot(.) to finish:\n";
do{
c = cin.get();
str_E += c;
if(c=='\n'){
cout<<str_E;
str_E.clear();
}
}while(c!='.');
//compare 方法: 字符串的比较
string str_F("green apple");
string str_G("red apple");
if(str_F.compare(str_G) != 0){
cout<<str_F<<" is not "<<str_G<<'\n';
}
if(str_F.compare(6, 5, "apple") == 0){ //从字符串str_F的第 6 个位置往后的连续5个字符
cout<<"still, "<<str_F<<" is an apple\n";
}
if(str_G.compare(str_G.size()-5, 5, "apple") == 0){ //从字符串str_G的第 4 个位置往后的连续5个字符
cout<<"and "<<str_G<<" is also an apple\n";
}
if(str_F.compare(6, 5, str_G, 4, 5) == 0){
cout<<"therefore, both are apples\n";
}
//copy 方法:Copy sequence of characters from string,The function does not append a null character at the end of the copied content
//赋值后的字符串需要手动在末尾添加'\0'
char buffer[20];
string str_H("Test string...");
size_t length = str_H.copy(buffer, 6, 5);
buffer[length] = '\0';
cout<<"buffer contains: "<<buffer<<'\n';
//rbegin, rend方法:Return reverse iterator to reverse beginning
string str_Ii = "now step live...";
for(string::reverse_iterator rit = str_Ii.rbegin();rit != str_Ii.rend();++rit)
cout<<*rit;
cout<<'\n'; //...evil pets won
//crbegin , crend方法:Returns a const_reverse_iterator pointing to the last character of the string
//反向的起点
string str_I("lorem ipsum");
for(auto rit = str_I.crbegin();rit != str_I.crend();++rit){
cout<<*rit;
}
cout<<'\n'; //muspi merol
//c_str 方法:Returns a pointer to an array that contains a null-terminated sequence of characters
//This array includes the same sequence of characters that make up the value of the string object plus an additional terminating null-character ('\0') at the end
string str_J("Please split this sentence into tokens");
char *cstr = new char[str_J.length()+1];
strcpy(cstr, str_J.c_str());
// cstr now contains a c-string copy of str_J
char *p = strtok(cstr, " ");
while(p!=0){
cout<<p<<'\n';
p = strtok(NULL, " ");
}
delete[] cstr;
//data 方法:Return a pointer to the c-string representation of the string object's value
int length_K;
string str_K = "Test string";
char *cstr_k = "Test string"; //C++11 不支持string 到 char *的转换,可以编译通过但会warn
if( str_K.length() == strlen(cstr_k)){
cout<<"str_K and cstr_k have the same length.\n";
if(memcmp(cstr_k, str_K.data(), str_K.length()) == 0){
cout<<"str_K and cstr_k have the same content.\n";
}
}
//empty 方法:Test if string is empty,Returns whether the string is empty,true if the string length is 0, false otherwise
string content;
string line;
cout<<"Please introduce a text. Enter an empty line to finish:\n";
do{
getline(cin, line);
content += line + '\n';
}while(!line.empty());
cout<<"The text you introduced was:\n"<<content;
//find 方法:Searches the string for the first occurrence of the sequence specified by its arguments
//全词匹配
string str_L("There are two needls in this haystack with needles.");
string str_M("needls");
//different member versions of find in the same order as above:
size_t found = str_L.find(str_M);
if(found != string::npos)
cout<<"first 'needle' found at: "<<found<<'\n';
found = str_L.find("needles are small", found+1, 6); //意思是从str_L的第 15 个位置开始找出连续6个字符与"needles are small"有交集的子字符串,并返回这个子字符串的起始位置
if(found != string::npos)
cout<<"second 'needls' found at: "<<found<<'\n';
found = str_L.find("haystack");
if(found != string::npos)
cout<<"'haystack' also found at: "<<found<<'\n';
found = str_L.find('.');
if(found != string::npos)
cout<<"Period found at: "<<found<<'\n';
//rfind 方法:Searches the string for the last occurrence of the sequence specified by its arguments
string str_Li("The sixth sick sheik's sixth sheep's sick.");
string key("sixth");
size_t found_li = str_Li.rfind(key);
if(found != string::npos)
str_Li.replace(found_li, key.length(), "seventh");
cout<<str_Li<<'\n'; //The sixth sick sheik's seventh sheep's sick.
//下面有几个方法可以用到加密解密里面
//find_first_not_of 方法:Searches the string for the first character that does not match any of the characters specified in its arguments
//找到一个与匹配字符串任何字符都不匹配的字符的位置
string str_N("look for non-alphabetic characters...");
size_t found_N = str_N.find_first_not_of("abcdefghijklmnopqrstuvwxyz ");
if(found_N != string::npos){
cout<<"The first non-alphabetic character is "<<str_N[found_N]; //'-'
cout<<" at position "<<found_N<<'\n';
}
//find_first_of 方法:Searches the string for the first character that matches any of the characters specified in its arguments
string str_O("Please, replace the vowels in this sentence by asterisks.");
size_t found_O = str_O.find_first_of("aeiou");
while(found_O != string::npos){
str_O[found_O] = '*';
found_O = str_O.find_first_of("aeiou", found_O+1);
}
cout<<str_O<<'\n'; //Pl**s*, r*pl*c* th* v*w*ls *n th*s s*nt*nc* by *st*r*sks.
//find_last_not_of 方法: Find non-matching character in string from the end
string str_P("Please, erase trailing white-spaces \n");
string whitespaces(" \t\f\v\n\r");
size_t found_p = str_P.find_last_not_of(whitespaces);
if(found_p != string::npos)
str_P.erase(found_p+1); //删掉非空格 等 字符 后面的所有字符
else
str_P.clear();
cout<<str_P<<endl; //"Please, erase trailing white-spaces"
//find_last_of 方法: Searches the string for the last character that matches any of the characters specified in its arguments.
string str_Q("/usr/bin/man");
string str_R("D:\androidSDK\\emulator\\emulator.exe");
SplitFilename(str_Q);
SplitFilename(str_R);
//front 方法: Access first character.Returns a reference to the first character of the string
//Unlike member string::begin, which returns an iterator to this same character, this function returns a direct reference.
//This function shall not be called on empty strings
string str_S("test string");
str_S.front() = 'T';
cout<<str_S<<endl; //Test string
//pop_back 方法:Erases the last character of the string, effectively reducing its length by one
string str_T("hello world!");
str_T.pop_back();
cout<<str_T<<endl; //hello world
cout<<str_T.length()<<endl; //11
//push_back 方法:Appends character c to the end of the string, increasing its length by one
string str_U;
ifstream file("F:\\QtProj\\string_demo\\text.txt", ios::in);
if(file.is_open()){
//cout<<"ok..."<<endl;
while(!file.eof())
str_U.push_back(file.get()); //挨个字节文件数据写到str_U字符串中
}
cout<<str_U<<endl; //文件内容
//replace 方法:Replaces the portion of the string that begins at character pos and spans len characters
//替换从字符位置开始并跨越 len 长度字符的字符串部分
string base = "this is a test string";
string str_V1 = "n example";
string str_V2 = "sample phrase";
string str_V3 = "userful.";
string str_W = base;
str_W.replace(9, 5, str_V1); //将base字符串从第九个位置开始往后的连续5个位置的字符替换为str_V1
cout<<str_W<<endl; //this is an example string
str_W.replace(19, 6, str_V2, 7, 6); //将str_V2字符串的第7个位置往后的连续6个字符替换到str_W字符串的第19个位置往后的连续6个字符的位置
cout<<str_W<<endl; //this is an example phrase
str_W.replace(8, 10, "just a");
cout<<str_W<<endl; //this is just a phrase
str_W.replace(8, 6, "a shorty", 7); //将字符串"a shorty"中从0开始往后7个字节长度的部分替换到str_W的第8个字节开始往后的连续6个字符的位置
cout<<str_W<<endl; //this is a short phrase
str_W.replace(22, 1, 3, '!');
cout<<str_W<<endl; //this is a short phrase!!!
//Using iterators:
str_W.replace(str_W.begin(), str_W.end()-3, str_V2);
cout<<str_W<<endl; //sample phrase!!!
str_W.replace(str_W.begin(), str_W.begin()+6, "replace");
cout<<str_W<<endl; //replace phrase!!!
str_W.replace(str_W.begin()+8, str_W.begin()+14, "is coolness", 7); //7表示从 is coolness中从头开始取7个长度字符
cout<<str_W<<endl; //replace is cool!!!
str_W.replace(str_W.begin()+12, str_W.end()-4, 4, 'o');
cout<<str_W<<endl; //replace is cooool!!!
str_W.replace(str_W.begin()+11, str_W.end(), str_V3.begin(), str_V3.end());
cout<<str_W<<endl; //replace is userful.
//reserve 方法:Request a change in capacity
string str_X;
ifstream file_x("F:\\QtProj\\string_demo\\text.txt", ios::in|ios::ate);
if(file_x.is_open()){
ifstream::streampos filesize = file_x.tellg();
str_X.reserve(filesize);
file_x.seekg(0);
while(!file_x.eof()){
str_X += file_x.get();
}
cout<<str_X<<endl;
}
//resize 方法:Resizes the string to a length of n characters
string str_y("I like to code in C");
cout<<str_y<<'\n';
unsigned sz = str_y.size();
str_y.resize(sz+2, '+');
cout<<str_y<<endl; //I like to code in C++
str_y.resize(14);
cout<<str_y<<endl; //I like to code
//shrink_to_fit 方法:Requests the string to reduce its capacity to fit its size
//请求字符串减小其容量以适合其大小
//This function has no effect on the string length and cannot alter its content
string str_z(100, 'x');
cout<<str_z<<endl;
cout<<"1. capacity of str_z: "<<str_z.capacity()<<'\n'; //1. capacity of str_z: 100
str_z.resize(10);
cout<<"2. capacity of str_z: "<<str_z.capacity()<<'\n'; //2. capacity of str_z: 100
str_z.shrink_to_fit();
cout<<"3. capacity of str_z: "<<str_z.capacity()<<'\n'; //3. capacity of str_z: 15
//swap 方法:Exchanges the content of the container by the content of str, which is another string object. Lengths may differ
string buyer("money");
string seller("goods");
cout<<"Before the swap,buyer has "<<buyer;
cout<<" and seller has "<<seller<<'\n';
seller.swap(buyer);
cout<<"After the swap, buyer has "<<buyer;
cout<<" and seller has "<<seller<<'\n';
return 0;
}