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<title>Issue 2009: Reporting out-of-bound values on numeric string conversions</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#C++14">C++14</a> status.</em></p>
<h3 id="2009"><a href="lwg-defects.html#2009">2009</a>. Reporting out-of-bound values on numeric string conversions</h3>
<p><b>Section:</b> 27.4.5 <a href="https://wg21.link/string.conversions">[string.conversions]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2010-07-19 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#string.conversions">issues</a> in [string.conversions].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The functions (<code>w</code>)<code>stoi</code> and (<code>w</code>)<code>stof</code>
are specified in terms of calling C library APIs for potentially wider
types.  The integer and floating-point versions have subtly different
behaviour when reading values that are too large to convert.  The
floating point case will throw <code>out_of_bound</code> if the read value
is too large to convert to the wider type used in the implementation,
but behaviour is undefined if the converted value cannot narrow to a
float.  The integer case will throw <code>out_of_bounds</code> if the
converted value cannot be represented in the narrower type, but throws
<code>invalid_argument</code>, rather than <code>out_of_range</code>, if the
conversion to the wider type fails due to overflow.
</p>

<p>
Suggest that the Throws clause for both specifications should be
consistent, supporting the same set of fail-modes with the matching set
of exceptions.
</p>



<p id="res-2009"><b>Proposed resolution:</b></p>
<p>
21.5p3 [string.conversions]
</p>

<blockquote><pre>
int stoi(const string&amp; str, size_t *idx = 0, int base = 10);
long stol(const string&amp; str, size_t *idx = 0, int base = 10);
unsigned long stoul(const string&amp; str, size_t *idx = 0, int base = 10);
long long stoll(const string&amp; str, size_t *idx = 0, int base = 10);
unsigned long long stoull(const string&amp; str, size_t *idx = 0, int base = 10);
</pre>

<blockquote>
<p>
...
</p>
<p>
3 <i>Throws:</i> <code>invalid_argument</code> if <code>strtol</code>,
<code>strtoul</code>, <code>strtoll</code>, or <code>strtoull</code> reports that no
conversion could be performed. Throws <code>out_of_range</code> if
<ins><code>strtol</code>, <code>strtoul</code>, <code>strtoll</code> or
<code>strtoull</code> sets <code>errno</code> to <code>ERANGE</code>, or if</ins>
the converted value is outside the range of representable values for the
return type.
</p>
</blockquote>
</blockquote>

<p>
21.5p6 [string.conversions]
</p>

<blockquote><pre>
float stof(const string&amp; str, size_t *idx = 0);
double stod(const string&amp; str, size_t *idx = 0);
long double stold(const string&amp; str, size_t *idx = 0);
</pre>

<blockquote>
<p>
...
</p>
<p>
6 <i>Throws:</i> <code>invalid_argument</code> if <code>strtod</code> or
<code>strtold</code> reports that no conversion could be performed. Throws
<code>out_of_range</code> if <code>strtod</code> or <code>strtold</code> sets
<code>errno</code> to <code>ERANGE</code> <ins> or if the converted value is
outside the range of representable values for the return type</ins>.
</p>
</blockquote>
</blockquote>






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