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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - Clang ignores nonnull attributes on declarations following definitions when compiling as C++; behavior differs from gcc and EDG" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24134&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=MBbbafjpU12o_j6eJMwXEEqYmIwX1ulK4t-wKEvdEEA&s=t3I6rDgyOoQazY9x_Era5r6VJguPPQ2rq8tiWIAR9yc&e=">24134</a>
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<th>Summary</th>
<td>Clang ignores nonnull attributes on declarations following definitions when compiling as C++; behavior differs from gcc and EDG
</td>
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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>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>thonermann@coverity.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Clang (3.4-3.6,trunk) ignores nonnull attributes on declarations following
definitions when compiling as C++, but not as C. I presume the difference has
to do with tentative definitions in C.
A test case is below. Recent versions of gcc and EDG both allow nonnull
attributes on declarations following a definition, at least for this test case,
so this behavior appears to be inconsistent with other common compilers.
$ cat t.c
void (*pf)(int *p1);
extern void (*pf)(int *p1)
__attribute__((nonnull));
void f() {
pf(0);
}
# Compiling as C, no warning is emitted, the nonnull attribute
# is present in the resulting AST:
$ clang -c -Xclang -ast-dump t.c
t.c:5:9: warning: null passed to a callee that requires a non-null argument
[-Wnonnull]
pf(0);
~^
...
`-VarDecl 0x822dda0 prev 0x822dc50 <line:2:1, col:26> col:15 pf 'void (*)(int
*)' extern
`-NonNullAttr 0x822de00 <line:3:20>
...
# Compiling as C++, a warning is emitted and the nonnull attribute
# is not present in the resulting AST:
$ clang -c -Xclang -ast-dump -x c++ t.c
t.c:3:20: warning: attribute declaration must precede definition
[-Wignored-attributes]
__attribute__((nonnull));
^
t.c:1:8: note: previous definition is here
void (*pf)(int *p1);
^
...
`-VarDecl 0x82e41e0 prev 0x82e4090 <line:2:1, col:26> col:15 pf 'void (*)(int
*)' extern
...
1 warning generated.
# gcc (4.6.3) emits a warning when invoking *pf with a null argument regardless
of whether the code is compiled as C or C++:
$ gcc -Wall -c t.c
t.c: In function 'f':
t.c:5:5: warning: null argument where non-null required (argument 1)
[-Wnonnull]
$ gcc -Wall -c -x c++ t.c
t.c: In function 'void f()':
t.c:5:9: warning: null argument where non-null required (argument 1)
[-Wnonnull]</pre>
</div>
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