https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87120
Bug ID: 87120
Summary: gcc incorrectly accepts uniform-initializing bool
values from double
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vz-gcc at zeitlins dot org
Target Milestone: ---
gcc 8.2.0 incorrectly (AFAICS) compiles the following program:
% cat -n init.cpp
1 double foo() { return 17.0; }
2
3 int main()
4 {
5 bool b{foo()};
6 return b;
7 }
% g++ -std=c++17 -Wall init.cpp
% g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.2.0-4'
--with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-8
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.2.0 (Debian 8.2.0-4)
Compare this with clang:
% clang++-7 -std=c++17 -Wall init.cpp && ./a.out
init.cpp:5:12: error: type 'double' cannot be narrowed to 'bool' in initializer
list [-Wc++11-narrowing]
bool b{foo()};
^~~~~
init.cpp:5:12: note: insert an explicit cast to silence this issue
bool b{foo()};
^~~~~
static_cast<bool>( )
1 error generated.
or MSVS 2017.7:
% cl /W4 init.cpp
init.cpp
init.cpp(5): error C2397: conversion from 'double' to 'bool' requires a
narrowing conversion
