https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125371
Bug ID: 125371
Summary: Missing fixit hint for forward declaration w/
std::istringstream and missing <sstream> include
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sjames at gcc dot gnu.org
Target Milestone: ---
The forward declaration here comes from libstdc++ headers (don't think I'd
expect one if the user had done it):
```
#include <fstream>
int main() {
std::string line;
std::istringstream foo(line);
}
```
```
$ g++ a.cxx
a.cxx: In function ‘int main()’:
a.cxx:5:36: error: variable ‘std::istringstream foo’ has initializer but
incomplete type
5 | std::istringstream foo(line);
| ^
```
We should suggest `#include <sstream>`.
```
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/17/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage.notmp/portage/sys-devel/gcc-17.0.9999/work/gcc-17.0.9999/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/17
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/17/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/17
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/17/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/17/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/17/include/g++-v17
--disable-silent-rules --disable-dependency-tracking
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/17/python
--enable-libphobos --enable-objc-gc
--enable-languages=c,c++,d,objc,obj-c++,fortran,ada,algol68,m2,jit
--enable-obsolete --enable-secureplt --disable-werror --with-system-zlib
--enable-nls --without-included-gettext --disable-libunwind-exceptions
--enable-checking=yes,extra,rtl --with-bugurl=https://bugs.gentoo.org/
--with-pkgversion='Gentoo Hardened 17.0.9999 p, commit
5e0f4dab67e423788db0d3858125bdbe8b2e3779' --with-gcc-major-version-only
--enable-libstdcxx-time --enable-lto --disable-libstdcxx-pch
--enable-linker-build-id --enable-libada --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu --with-tls=gnu2 --enable-multilib
--with-multilib-list=m32,mx32,m64 --disable-fixed-point --with-abi=m64
--enable-targets=all --enable-offload-defaulted
--enable-offload-targets=nvptx-none --enable-libgomp --disable-libssp
--disable-cet --enable-systemtap --enable-valgrind-annotations
--enable-valgrind-interop --disable-vtable-verify --disable-libvtv --with-zstd
--with-isl --disable-isl-version-check --enable-default-pie --enable-host-pie
--enable-host-bind-now --enable-default-ssp --disable-fixincludes
--with-gxx-libcxx-include-dir=/usr/include/c++/v1 --enable-host-shared
--enable-libgdiagnostics --with-build-config='bootstrap-O3 bootstrap-lto-lean'
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 17.0.0 20260518 (experimental)
c0fd049ae75349dc273de868fd3b3e8935115418 (Gentoo Hardened 17.0.9999 p, commit
5e0f4dab67e423788db0d3858125bdbe8b2e3779)
```
