stoi

stoi() 函数的形参类型是const string*

atoi

atoi() 函数的形参类型是const char*, 可以用c_str()函数进行类型转换。

#include <iostream>  
#include <string>  
using namespace std;
int main() {

  string s1 = "2147482", s2 = "-214748"; 
  string s3 = "214748666666663", s4 = "-21474836488"; 
  cout << stoi(s1) << endl; 
  cout << stoi(s2) << endl; 
  cout << atoi(s3.c_str()) << endl; 
  cout << atoi(s4.c_str()) << endl; 
  return 0;
}

strncpy

strncpy() 函数的形参类型是char*.
reference:
https://blog.csdn.net/yky__xukai/article/details/79554963