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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - false positive, -Wsign-conversion, it is known that signed value is positive" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24037&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=6Vz5fLEY3VTqJvUF6xiJnNvavBE_WFn1WX3zi49pLpA&s=sgX6FwQvNNevKhZcJylQf5HK7U47jxjDCbu0BeOtcy4&e=">24037</a>
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<th>Summary</th>
<td>false positive, -Wsign-conversion, it is known that signed value is positive
</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>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>daniel.marjamaki@evidente.se
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Example code:
#include <string>
void f(int x, std::string s) {
if (x >= 0)
s[x] = 'x'; // <- warning about x
}
Clang writes this false positive:
signconv.cpp:21:9: warning: implicit conversion changes signedness: 'int' to
'size_type' (aka 'unsigned long') [-Wsign-conversion]
s[x] = 'x';
~ ^
it is obvious that x is positive. therefore this is a false positive. the
implicit cast is not bad.
In this code example the dangerous casts has been taken care of properly.
Adding a cast instead is the wrong solution. However adding a cast is the
recommended approach by the checker - that is the only way to fix this warning.
This kind of false positive is indirectly a security problem. People routinely
hide these false positives using casts or changed variable types etc. and that
cause bugs and hides other real warnings.</pre>
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