https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85749
Bug ID: 85749 Summary: Possible -Wsign-conversion false negative with std::default_random_engine Product: gcc Version: 7.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: martingalvan at sourceware dot org Target Milestone: --- I have the following code: #include <chrono> #include <random> int main() { const auto seed = std::chrono::system_clock::now().time_since_epoch().count(); std::default_random_engine generator(seed); generator.seed(seed); return 0; } If I build this using g++ -std=c++17 -Wsign-conversion -o random random.cpp, I get the following warning: random.cpp: In function ‘int main()’: random.cpp:9:24: warning: conversion to ‘std::linear_congruential_engine<long unsigned int, 16807, 0, 2147483647>::result_type {aka long unsigned int}’ from ‘long int’ may change the sign of the result [-Wsign-conversion] generator.seed(seed); However, AFAIK the std::default_random_engine constructor also takes a result_type (which should be unsigned). Therefore, the warning should also come up when constructing 'generator'. $ g++ -v Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.2.0-8ubuntu3.2' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --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 7.2.0 (Ubuntu 7.2.0-8ubuntu3.2)