简单的字符串替换给出错误，尽管参数正确

我正在尝试使用以下代码使用此处给出的详细信息替换字符串的一部分：

#include <iostream>
#include <string>
using namespace std ; 
int main(){
string ori = "this is a test"; // to replace "is a" with "IS A"
string part = "is a"; 
int posn = ori.find(part); 
int len = part.size(); 
cout << posn << endl; 
ori.replace(posn, len, ori, "IS A"); 
cout << ori; 
}

但是，它给出一个很长的错误，开头为：

rnreplacestr.cpp:11:36: error: no matching function for call to ‘std::__cxx11::basic_string<char>::replace(int&, int&, std::__cxx11::string&, const char [5])’
ori.replace(posn, len, ori, "IS A");
^
In file included from /usr/include/c++/6/string:52:0,
from /usr/include/c++/6/bits/locale_classes.h:40,
from /usr/include/c++/6/bits/ios_base.h:41,
from /usr/include/c++/6/ios:42,
from /usr/include/c++/6/ostream:38,
from /usr/include/c++/6/iostream:39,
from rnreplacestr.cpp:1:

问题出在哪里，如何解决？感谢您的帮助。