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The Since std::basic_string is a container of characters, this rule is a specific instance of CTR51-CPP. Use valid references, pointers, and iterators to reference elements of a container. As a container, it supports iterators just like other containers in the Standard Template Library. However, the std::basic_string template class has unusual invalidation semantics. According to the C++ Standard, [string.require], paragraph 5 [ISO/IEC 14882-2014]:

References, pointers, and iterators referring to the elements of a basic_string sequence may be invalidated by the following uses of that basic_string object:

• As an argument to any standard library function taking a reference to non-const basic_string as an argument.
• Calling non-const member functions, except operator[], at, front, back, begin, rbegin, end, and rend.

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Do not use an invalidated reference, pointer, or iterator because doing so results in undefined behavior.Since std::basic_string is a container of characters, 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 semicolon (;) 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.

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

Noncompliant Code Example

In this noncompliant code example, data is invalidated after the call to replace(), and so its use in g() is undefined behavior:

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