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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __FILE__ is modified whenever "#include __FILE__" is encountered"
href="https://bugs.llvm.org/show_bug.cgi?id=44480">44480</a>
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<th>Summary</th>
<td>__FILE__ is modified whenever "#include __FILE__" is encountered
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>9.0
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>omoikane@uguu.org
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Created <span class=""><a href="attachment.cgi?id=22994" name="attach_22994" title="Demonstration of how __FILE__ is modified">attachment 22994</a> <a href="attachment.cgi?id=22994&action=edit" title="Demonstration of how __FILE__ is modified">[details]</a></span>
Demonstration of how __FILE__ is modified
Clang's preprocessor appears to prepend "./" to __FILE__ every time it
encounters "#include __FILE__" in a source code. This can be observed by how 3
different strings are printed for this code:
#ifndef INCLUDE_GUARD
#define INCLUDE_GUARD
#include <stdio.h>
int main(int argc, char **argv)
{
puts(__FILE__);
#include __FILE__
puts(__FILE__);
#include __FILE__
puts(__FILE__);
return 0;
}
#endif
<a href="https://gcc.godbolt.org/z/JTx2Np">https://gcc.godbolt.org/z/JTx2Np</a>
If a piece of code manages to #include itself a finite but large number of
times, "#include __FILE__" will eventually fail because __FILE__ contains a
string longer than what's supported by the local file system.
The preprocessor should just keep __FILE__ constant. Clang 3.5.1 and earlier
and all versions of GCC has the expected behavior, Clang 3.6 and later appears
to modify __FILE__.</pre>
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