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Do not use a reference, pointer, or iterator that has been invalidated, as that results in undefined behavior. This rule is a specific instance of CTR51-CPP. Use valid references, pointers, and iterators to reference elements of a container.

Noncompliant Code Example

This noncompliant code example copies input into a std::string, replacing ';' characters with spaces. This example is noncompliant because the iterator loc is invalidated after the first call to insert(). The behavior of subsequent calls to insert() is undefined.

#include <string>
 
void f(const std::string &input) {
  std::string email;
  std::string::iterator loc = email.begin();

  // copy input into email converting ";" to " "
  for (auto I = input.begin(), E = input.end(); I != E; ++I, ++loc) {
    email.insert(loc, *I != ';' ? *I : ' ');
  }
}

Compliant Solution (std::string::insert())

In this compliant solution, the value of the iterator loc is updated as a result of each call to insert() so that the invalidated iterator is never accessed. The updated iterator is then incremented at the end of the loop.

#include <string>
 
void f(const std::string &input) {
  std::string email;
  std::string::iterator loc = email.begin();

  // copy input into email converting ";" to " "
  for (auto I = input.begin(), E = input.end(); I != E; ++I, ++loc) {
    loc = email.insert(loc, *I != ';' ? *I : ' ');
  }
}

Compliant Solution (std::replace())

In this compliant solution, the manual loop is replaced with a standard algorithm that performs the replacement. Using generic algorithms is generally preferable to inventing your own solution when possible.

#include <algorithm>
#include <string>
 
void f(const std::string &input) {
  std::string email{input};
  std::replace(email.begin(), email.end(), ';', ' ');
}

Risk Assessment

Using an invalid reference, pointer or iterator to a string object could allow an attacker to run arbitrary code.

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Bibliography

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