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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - adding zero to null pointer rejected in constant expressions"
href="http://llvm.org/bugs/show_bug.cgi?id=19346">19346</a>
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<th>Summary</th>
<td>adding zero to null pointer rejected in constant expressions
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++11
</td>
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<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>zilla@kayari.org
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
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</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>constexpr int* p = nullptr;
constexpr int n = 0;
constexpr int* p2 = p + n;
a.cc:3:16: error: constexpr variable 'p2' must be initialized by a constant
expression
constexpr int* p2 = p + n;
^ ~~~~~
a.cc:3:23: note: cannot perform pointer arithmetic on null pointer
constexpr int* p2 = p + n;
^
Th last paragraph of [expr.add] says "If the value 0 is added to or subtracted
from a pointer value, the result compares equal to the original pointer value."
I believe that should also apply for a null pointer.
Rejecting this makes it more awkward to define end() in the code below:
struct initializer_list {
constexpr initializer_list() : b(nullptr), sz(0) { }
constexpr int* begin() const { return b; }
constexpr int* end() const { return b+sz; }
int* b;
unsigned sz;
};
constexpr initializer_list il;
constexpr int* p = il.end();</pre>
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