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6    The C and POSIX standards guarantee that <code class="varname">errno</code>
7    is never set to zero by any library function.
8    The C++ standard has less to say about when <code class="varname">errno</code>
9    is or isn't set, but libstdc++ follows the same rule and never sets
10    it to zero.
11  </p><p>
12    On the other hand, there are few guarantees about when the C++ library
13    sets <code class="varname">errno</code> on error, beyond what is specified for
14    functions that come from the C library.
15    For example, when <code class="function">std::stoi</code> throws an exception of
16    type <code class="classname">std::out_of_range</code>, <code class="varname">errno</code>
17    may or may not have been set to <code class="constant">ERANGE</code>.
18  </p><p>
19    Parts of the C++ library may be implemented in terms of C library
20    functions, which may result in <code class="varname">errno</code> being set
21    with no explicit call to a C function. For example, on a target where
22    <code class="function">operator new</code> uses <code class="function">malloc</code>
23    a failed memory allocation with <code class="function">operator new</code> might
24    set <code class="varname">errno</code> to <code class="constant">ENOMEM</code>.
25    Which C++ library functions can set <code class="varname">errno</code> in this way
26    is unspecified because it may vary between platforms and between releases.
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