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<title>Issue 83: String::npos vs. string::max_size()</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#TC1">TC1</a> status.</em></p>
<h3 id="83"><a href="lwg-defects.html#83">83</a>. String::npos vs. string::max_size()</h3>
<p><b>Section:</b> 27.4.3 <a href="https://wg21.link/basic.string">[basic.string]</a> <b>Status:</b> <a href="lwg-active.html#TC1">TC1</a>
 <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#basic.string">active issues</a> in [basic.string].</p>
<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TC1">TC1</a> status.</p>
<p><b>Duplicate of:</b> <a href="lwg-closed.html#89" title="Missing throw specification for string::insert() and string::replace() (Status: Dup)">89</a></p>
<p><b>Discussion:</b></p>
<p>Many string member functions throw if size is getting or exceeding
npos. However, I wonder why they don't throw if size is getting or
exceeding max_size() instead of npos.  May be npos is known at compile
time, while max_size() is known at runtime. However, what happens if
size exceeds max_size() but not npos, then? It seems the standard
lacks some clarifications here.</p>


<p id="res-83"><b>Proposed resolution:</b></p>
<p>After 27.4.3 <a href="https://wg21.link/basic.string">[basic.string]</a> paragraph 4 (&quot;The functions
described in this clause...&quot;) add a new paragraph:</p>

<blockquote>
  <p>For any string operation, if as a result of the operation, <code> size()</code> would exceed
  <code> max_size()</code> then
  the operation throws <code>length_error</code>.</p>
</blockquote>


<p><b>Rationale:</b></p>
<p>The LWG believes length_error is the correct exception to throw.</p>




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