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daviddoria/gist:0e28d5d39b3a59afaec5f892e67f27c5

Created December 10, 2016 02:39
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gistfile1.txt
original
------------
/usr/include/c++/6.1.1
/usr/include/c++/6.1.1/x86_64-pc-linux-gnu
/usr/include/c++/6.1.1/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/include-fixed
/usr/include
(/usr/include is a system directory; the -I argument does nothing.)
cmath is at the path /usr/include/c++/6.1.1/cmath, which is the first element of the search path. math.h can be found in
/usr/include/math.h
/usr/include/c++/6.1.1/math.h
The use of #include_next <math.h> in cmath ensures that the copy of math.h in /usr/include/c++/6.1.1 is skipped and that the copy used is /usr/include/math.h.
With g++ -isystem /usr/include, the search path is
updated
--------------------
/usr/include/c++/6.1.1
/usr/include/c++/6.1.1/x86_64-pc-linux-gnu
/usr/include/c++/6.1.1/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/include-fixed
/usr/include
(/usr/include is a system directory; the -I argument does nothing.)
cmath is at the path /usr/include/c++/6.1.1/cmath, which is the first element of the search path. math.h can be found in:
/usr/include/c++/6.1.1/math.h (the same directory of the cmath we are considering)
and
/usr/include/math.h
The use of `#include_next <math.h>` in cmath ensures that the copy of math.h in /usr/include/c++/6.1.1 is skipped and that the copy used is /usr/include/math.h.
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