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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ostream writes a double that istream can't read"
href="https://bugs.llvm.org/show_bug.cgi?id=39012">39012</a>
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<th>Summary</th>
<td>ostream writes a double that istream can't read
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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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>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>daniel.cooke@me.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>It appears libc++ incorrectly sets input stream failbit when reading subnormal
floating point numbers. Here's an example:
#include <iostream>
#include <string>
#include <sstream>
int main()
{
constexpr double x {1e-320};
std::ostringstream oss {};
oss << x;
const auto str_x = oss.str();
std::istringstream iss {str_x};
double y;
if (iss >> y) {
std::cout << y << std::endl;
} else {
std::cout << "Nope" << std::endl;
}
}
Compiling with Clang/libc++, results in "Nope" being printed, while with
GCC/libstdc++, the value of the double is printed - as I would expect.
I also reported this behaviour in StackOverflow:
<a href="https://stackoverflow.com/questions/52410931/why-does-clang-stdostream-write-a-double-that-stdistream-cant-read">https://stackoverflow.com/questions/52410931/why-does-clang-stdostream-write-a-double-that-stdistream-cant-read</a>.</pre>
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