**`npos`** is a constant static member value with the *greatest possible* value for an element of type *size_t*.

This value, when used as the value for a len parameter in string's member functions, means *until the end of the string*. This constant is defined with a value of -1. 
Since size_t is an unsigned integral type, -1 is the largest possible representable value for this type.

To put it simply, think of npos as *no-position*. As a return value, it is usually used to indicate that no matches were found in the string. Thus, if it returns true, matches were found at no positions (i.e., no matches).


#include <iostream>
using namespace std;

int main() {
  
  string str2 = "app";
  string str = "an apple";
  
  int found=str.find(str2);

  if (found != string::npos){
    cout << "first 'app' found at: " << int(found) << endl;
  }
}

What is string::npos in C++?

npos represents the largest possible size_t value, indicating no matches or end of a string.

What is string::npos in C++?

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