例子
1
#include <iostream>
2#include <string>
3
4using namespace std;
5int main()
6
{
7
string st="ifn",b;
8 b=st.substr(0,2);
9 cout<<b<<endl;
10 return 0;
11
12
}
#include <iostream>2
#include <string>3
4
using namespace std;5
int main()6
{ 
7
string st="ifn",b; 8
b=st.substr(0,2); 9
cout<<b<<endl; 10
return 0;11
12
}
结果 if
basic_string substr(size_type pos = 0, size_type n = npos) const;
The member function returns an object whose controlled sequence is a copy of up to n elements of the controlled sequence beginning at position pos.
substr(start,length);
带两个参数，第一个是子串的起始位置（从0开始），第二个是子串的长度
