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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Wrong "warning: subtraction of pointers to type 'int [n]' of zero size has undefined behavior [-Wpointer-arith]""
href="https://llvm.org/bugs/show_bug.cgi?id=27954">27954</a>
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<th>Summary</th>
<td>Wrong "warning: subtraction of pointers to type 'int [n]' of zero size has undefined behavior [-Wpointer-arith]"
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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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>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>cherepan@mccme.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Source code:
----------------------------------------------------------------------
#include <stdio.h>
int main()
{
int n = 1;
int a[n];
(void)(&a + 1 - &a);
printf("sizeof(int [n]) = %zu\n", sizeof(int [n]));
}
----------------------------------------------------------------------
Results:
----------------------------------------------------------------------
$ clang -std=c11 -Weverything -Wno-vla -O3 test.c && ./a.out
test.c:7:17: warning: subtraction of pointers to type 'int [n]' of zero size
has undefined behavior [-Wpointer-arith]
(void)(&a + 1 - &a);
~~~~~~ ^ ~~
1 warning generated.
sizeof(int [n]) = 4
----------------------------------------------------------------------
clang version: clang version 3.9.0 (trunk 271312)
The warning talks about zero size but the size of type 'int [n]' is not zero as
illustrated by the result of printf. The warning is wrong.</pre>
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