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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - False positive on reading undefined value from streams"
href="https://bugs.llvm.org/show_bug.cgi?id=34817">34817</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>False positive on reading undefined value from streams
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</td>
</tr>
<tr>
<th>OS</th>
<td>MacOS X
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Static Analyzer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>kremenek@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>howard.hinnant@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This code gets an analyzer warning:
#include <cassert>
#include <sstream>
int
main()
{
std::istringstream in{""};
char c;
in >> c;
assert(!in.fail());
return int{c};
}
scan-build: Using '/Users/howardhinnant/Development/llvm_build/bin/clang-6.0'
for static analysis
test.cpp:492:5: warning: Undefined or garbage value returned to caller
return int{c};
^~~~~~~~~~~~~
1 warning generated.
scan-build: 1 bug found.
scan-build: Run 'scan-view
/var/folders/7d/bq37f_s53dbgw_z48smv9q9m0000gn/T/scan-build-2017-10-03-121247-59896-1'
to examine bug reports.
It would be nice if the analyzer could detect that c can't be garbage because
in.fail() is checked and if true never reaches the use of c.
Even better would be this:
#include <cassert>
#include <sstream>
int
main()
{
std::istringstream in{""};
in.exceptions(std::ios::failbit | std::ios::badbit);
assert(((std::ios::failbit | std::ios::badbit) & in.exceptions()) ==
(std::ios::failbit | std::ios::badbit));
char c;
in >> c;
return int{c};
}
c can not be used with garbage, proven by the settings in in.exceptions(). So
no warning on the above either.</pre>
</div>
</p>
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