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    <p>The title of your question references C strings. C++ <code>std::string</code> objects are handled differently than <em>standard C</em> strings. <code>\0</code> is important when using C strings, and when I use the term <code>string</code> here, I'm referring to <em>standard C strings</em>.</p> <p><code>\0</code> acts as a string terminator in C. It is known as the <em>null character</em>, or <em>NUL</em>. It signals code that processes strings - standard libraries but also your own code - where the end of a string is. A good example is <code>strlen</code> which returns the length of a string.</p> <p>When you declare a constant string with:</p> <pre><code>const char *str = "JustAString"; </code></pre> <p>then the <code>\0</code> is appended automatically for you. In other cases, where you'll be managing a non-constant string as with your array example, you'll sometimes need to deal with it yourself. The <a href="http://en.cppreference.com/w/c/string/byte/strncpy">docs for strncpy</a>, which is used in your example, are a good illustration: <code>strncpy</code> copies over the null termination characters <strong>except</strong> in the case where the specified length is reached before the entire string is copied. Hence you'll often see <code>strncpy</code> combined with the <em>possibly redundant</em> assignment of a null terminator. <code>strlcpy</code> and <code>strcpy_s</code> were designed to address the potential problems that arise from neglecting to handle this case.</p> <p>In your particular example, <code>array[s.size()] = '\0';</code> is one such redundancy: since <code>array</code> is of size <code>s.size() + 1</code>, and <code>strncpy</code> is copying <code>s.size()</code> characters, the function will append the <code>\0</code>.</p> <p>The documentation for standard C string utilities will indicate when you'll need to be careful to include such a null terminator. But read the documentation carefully: as with <code>strncpy</code> the details are easily overlooked, leading to potential buffer overflows.</p>
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