c++字符串函数 --- substr()函数的用法

#include<string>
#include<iostream>
using namespace std;
int main()
{
　　string s("12345asdf");
　　string a = s.substr(0,5);     //获得字符串s中从第0位开始的长度为5的字符串
　　cout << a << endl;
}

#include<bits/stdc++.h>

using namespace std;

int main(){
    string s1,s2;
	while(cin>>s1>>s2){
	int l1 = s1.size();
	int l2 = s2.size();
	bool flag = 0;
    for(int i=0;i<l1-l2+1;i++){
    	string s3 = s1.substr(i,l2);
    	if(s3 == s2){
    	flag = 1;
    	cout<<i+1<<endl;
		}
	}
	if(!flag) cout<<"0"<<endl;	
	}
	return 0;
}