On 6/12/2018 7:11 PM, Christian Franke wrote:
Ivan Shynkarenka wrote:
Could reproduce this with 32 and 64 bit Cygwin g++ 7.3.0
A comparison of preprocessor (-E) outputs shows that the "extern
template" declarations for getline() are only visible for C++ <= 14.
These are guarded by "__cplusplus <= 1402" in basic_string.tcc. This
should tell the compiler to generate new code for getline() if C++17 is
enabled instead of calling the (now incompatible) function in
cygstdc++-6.dll.
A comparison of assembly (-S) outputs shows that this does not work: If
C++17 is enabled, the compiler correctly generates local code for
getline(istream &, string &) but this code calls an external
getline(istream &, string &, char). Then the linker generates a call to
this getline() in cygstdc++-6.dll.
This is because there is a bogus prototype specialization for
getline(istream &, string &, char) in basic_string.h but no
corresponding implementation in basic_string.tcc. This has apparently an
equivalent effect as 'extern template'.
The attached patch for
/usr/lib/gcc/*-pc-cygwin/7.3.0/include/c++/bits/basic_string.h
fixes this.
Christian
Thanks Christian
for the investigation.
It seems an upstream bug so could you report it there ?
There are several c++17 bugs around
https://gcc.gnu.org/bugzilla/buglist.cgi?quicksearch=c%2B%2B17
that is probably the reason why gcc 7.x defaults to c++14
Regards
Marco
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