https://bugs.llvm.org/show_bug.cgi?id=44480
Bug ID: 44480
Summary: __FILE__ is modified whenever "#include __FILE__" is
encountered
Product: clang
Version: 9.0
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected],
[email protected]
Created attachment 22994
--> https://bugs.llvm.org/attachment.cgi?id=22994&action=edit
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
https://gcc.godbolt.org/z/JTx2Np
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__.
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