字符串的题目大多是和模拟题挂钩，处理起来很麻烦，除非使用正则表达式，但是那玩意又很恶心。所以今天下午我就总结了一下C++里面关于字符串常用的方法，干货满满哦！
#include<iostream>
#include<string>
#include<sstream>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
int main(){
cout<<"Commonly used string extraction methods\n";
string s="xuhacker ni hao";
string s1="h";
string s3="zxcvbnm,./";
unsigned long long i;
//string s.find(s1,pos) return the location where s1 first appeared, and if pos does not exist, the default value of pos is zero
if(s.find(s1)!=string::npos){
i=s.find(s1);
cout<<"the first position is: "<<i<<endl;
i=s.find(s1,6);
cout<<"the second postion is: "<<i<<endl;//return 12 if s1 does not exit ,retrun npos= 4294967295
}
//string s.erase
//the first use of string.erase();
s.erase(0,2);//return "hacker ni hao" -> Remove two characters from 0
cout<<"the first use of erase is "<<s<<endl;
//the second use of string.erase()
s.erase(5);//return hacke
cout<<"the second use of erase is "<<s<<endl;
//the third use of string.erase()
string::iterator it;//the iterator of string
it=s.begin()+2;
s.erase(it);//the position is an iterator ,meanwhile,remove the element of this position return "hake"
cout<<"the third use of erase is "<<s<<endl;
//the fourth use of string erase();
string::iterator first,last;
first=s.begin()+1;
last=s.end()-1;
s.erase(first,last);//Remove the elements between first and second, including first and last
cout<<"the fourth use of erase is "<<s<<endl;
//the use of substr()
//the first use of substr()
string s4=s3.substr(6);//return "m,./"
cout<<"the first use of substr is "<<s4<<endl;
string s5=s3.substr(6,2);//return "m,"
cout<<"the second use of substr is "<<s5<<endl;
string s6="asdf";
string s7=s5.insert(1,s6);//insert s6 to the position of 1
cout<<"s5 insert to s6 is "<<s7<<endl;
//the second use of insert
string::iterator it1;
it1=s5.begin();
s5.insert(it1,s7.begin()+1,s7.end()-1);
cout<<"the second use of insert is "<<s5<<endl;
//replace() which is in the algorithm
string s_replace="1231131132/163.com";
cout<<"old s_replace is: "<<s_replace<<endl;
replace(s_replace.begin(),s_replace.end(),'/','@');
cout<<"new s_replace is: "<<s_replace<<endl;
//s_replace.replace(pos,len,string);
s_replace.replace(3,5,"xu");
cout<<"s_replace.replace() is: "<<s_replace<<endl;
cout<<"=================sstream==================\n";
//the use of istringstream :to separate each substring of an entire string read in with a space
string s8="xuhacker . me";
istringstream iss;
iss.str(s8);
//int len=s8.length();
for(i=0;i<3;i++){
string value;
iss>>value;
cout<<"print this value: "<<value<<"\n";
}
cout<<"print the str in iss "<<iss.str()<<"\n";
//the use of ostringstream :
ostringstream oss;
oss<<"the use of oss is "<<s8<<endl;
cout<<oss.str();
//if you want to use oss again, you should clear it.
oss.clear();
//string s9=" ";
oss.str("");
cout<<"test it again (there is nothing :)"<<oss.str()<<endl;
//the use of stringstream:int to string
stringstream ss;
string s9;
int val=77;
ss<<val;//puts val
ss>>s9;//transform
cout<<"transform s9: "<<s9<<endl;
//the use of ss: string to int (twice),need use clear() there;
int a=0,b=0;
ss.clear();//"ss<<val" has used
ss<<"123";//puts the string
ss>> a;
cout<<"a is: "<<a<<endl;
// because "ss>>a" has used
ss.clear();
ss<<"234";
ss>>b;
cout<<"b is: "<<b<<endl;
cout<<"=============cstring==============\n";
char s11[100];
string s10;
getchar();
getline(cin,s10);//read a line same as "get(s11)"
//strcmp()
if(s10=="xu"/*strcmp(s11,"xu")*/)
cout<<"The two equal!!!\n";
else
cout<<"they are not equal!!!\n";
//strcpy()
s10="Yo.";/*The assignment strcpy(s11,"Yo.")*/
cout<<"S10 assigned values! s10 is: "<<s10<<"\n";
strcpy(s11,"Yo.");
cout<<"S11 assigned values! s11 is: "<<s11<<"\n";
//strcat()
s10+="Come on,xu!";
cout<<"s10 has connected with a new string,it is: "<<s10<<endl;
strcat(s11,"Come on,xu!") ;
cout<<"s11 has connected with a new string,it is: "<<s11<<endl;
//strtok();
char s12[]="xuhacker-me-hello-world";
char *t=strtok(s12,"-");//Cut the parent string into substrings
cout<<"After cutting the string: ";
while(t){
cout<<t<<" ";
t=strtok(NULL,"-");
}
cout<<endl;
//sscanf、sprintf same as sstream
cout<<"====================cctype========================"<<endl;
//isalpha : isdigit、 isupper 、islower、istolower、(to small)、istoupper(to big)
string s13="123alpha232./.";
for(int i=0;i<s13.length();i++){
if(isalpha(s13[i])){
cout<<s13[i]<<" ";
}
}
cout<<endl;
cout<<"all those funs are used to judge a string or a char\n";
return 0;
}
运行结果：
TIM截图20181124182930_test.png
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