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Because the input is unbounded, the following code could lead to a buffer overflow:.

#include <iostream>
 
void f() {
  char buf[12];
  std::cin >> buf;
}

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To solve this problem, it may be tempting to use the std::ios_base::width() method, but there still is a trap, as shown in this noncompliant code example:.

#include <iostream>
 
void f() {
  char bufOne[12];
  char bufTwo[12];
  std::cin.width(12);
  std::cin >> bufOne;
  std::cin >> bufTwo;
}

In this example, the first read will not overflow, but could fill bufOne with a truncated string. Furthermore, the second read still could overflow bufTwo. The C++ Standard, [istream.extractors], paragraphs 7–9, describes the behavior of operator>>(basic_istream &, charT *) and, and states in part [ISO/IEC 14882-2014], states the following:

operator>> then stores a null byte (charT()) in the next position, which may be the first position if no characters were extracted. operator>> then calls width(0).

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The best solution for ensuring that data is not truncated and for guarding against buffer overflows is to use std::string instead of a bounded array, as in this compliant solution:.

#include <iostream>
#include <string>
 
void f() {
  std::string input;
  std::string stringOne, stringTwo;
  std::cin >> stringOne >> stringTwo;
}

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