use wstring as input to stoull to make GCC 10.1.0 happy

[ekg]

I ran into a change in GCC behavior in 10.1.0.

Apparently, it's not possible to apply std::stoull to a regular std::string, and now std::wstring is required.

For instance

#include <iostream>
#include <string>                                                                                                                                                                               

uint64_t _parse_number(std::string::const_iterator& c, const std::string::const_iterator& end) {
    std::string::const_iterator s = c;
    while (c != end and isdigit(*c)) ++c;
    if (c > s) {
        return std::stoull(std::string(s,c));
    } else {
        return 0;                                                                                                                                                                                  
    }
}

int main(int argc, char** argv) {
    std::string s(argv[1]);
    std::string::const_iterator b = s.begin();
    std::string::const_iterator e = s.end();
    std::cout << _parse_number(b, e) << std::endl;
    return 0;
}

Compiling with GCC 10.1.0 gives this error:

-> % g++ test-stoull.cpp -o test-stoull
test-stoull.cpp: In function ‘uint64_t _parse_number(std::__cxx11::basic_string<char>::const_iterator&, const const_iterator&)’:                                                               test-stoull.cpp:13:33: error: invalid initialization of reference of type ‘const wstring&’ {aka ‘const std::__cxx11::basic_string<wchar_t>&’} from expression of type ‘std::string’ {aka ‘std::__cxx11::basic_string<char>’}
   13 |         return std::stoull(std::string(s,c));
      |                                 ^~~~~~~~~~~
In file included from /home/erikg/.guix-profile/include/c++/string:55,
                 from /home/erikg/.guix-profile/include/c++/bits/locale_classes.h:40,
                 from /home/erikg/.guix-profile/include/c++/bits/ios_base.h:41,
                 from /home/erikg/.guix-profile/include/c++/ios:42,
                 from /home/erikg/.guix-profile/include/c++/ostream:38,
                 from /home/erikg/.guix-profile/include/c++/iostream:39,
                 from test-stoull.cpp:1:
/home/erikg/.guix-profile/include/c++/bits/basic_string.h:6697:25: note: in passing argument 1 of ‘long long unsigned int std::__cxx11::stoull(const wstring&, std::size_t*, int)’
 6697 |   stoull(const wstring& __str, size_t* __idx = 0, int __base = 10)
      |          ~~~~~~~~~~~~~~~^~~~~

I get the same error when trying to compile sdsl-lite in this environment.

Changing the _parse_number code to use std::wstring resolves the issue. It might be less efficient, but I would expect things to work as before without issue. This patch does that within the io code.

I would be happy to hear that someone else can reproduce this. I didn't find much about wstring in the GCC release notes, and my environment is kind of funny (guix install).

[ekg]

Any thoughts on this?

[eloj]

This is most likely an issue with your environment/installation. The function should be overloaded so both std::string and std::wstring should work, and in fact, your example code compiles without error on my linux machine.

$ g++ test-stoull.cpp -o test-stoull
$ ./test-stoull hello
0
$ g++ -dumpversion
10.1.0

[ekg]

Thank you, I had trouble reproducing this too.

…

On Wed, May 27, 2020, 23:18 Eddy L O Jansson ***@***.***> wrote: This most likely an issue with your environment/installation. The function should be overloaded <https://en.cppreference.com/w/cpp/string/basic_string/stoul> so both std::string and std::wstring should work, and in fact, your example code compiles without error on my machine. $ g++ test-stoull.cpp -o test-stoull $ ./test-stoull hello 0 $ g++ -v Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/home/me/local/libexec/gcc/x86_64-linux-gnu/10.1.0/lto-wrapper Target: x86_64-linux-gnu Configured with: ../gcc-10.1.0/configure --enable-languages=c,c++ --prefix=/home/eddy/local/ --program-suffix=-10 --disable-nls --disable-multilib --with-system-zlib --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-cpu=native --with-arch=native --with-tune=native --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.1.0 (GCC) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#429 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABDQEJRLZ3RH6DONKOEJUDRTV7SHANCNFSM4NJLLLXA> .

[pjotrp]

For future reference: adding -D_GLIBCXX_USE_C99_STDLIB fixes the build:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 657949f..fcedbee 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -44,7 +44,7 @@ else()
 endif()

 if( CMAKE_COMPILER_IS_GNUCXX )
-    append_cxx_compiler_flags("-std=c++11 -Wall -Wextra -DNDEBUG" "GCC" CMAKE_CXX_FLAGS)
+    append_cxx_compiler_flags("-std=c++11 -D_GLIBCXX_USE_C99_STDLIB -Wall -Wextra -DNDEBUG" "GCC" CMAKE_CXX_FLAGS)
     append_cxx_compiler_flags("-O3 -ffast-math -funroll-loops" "GCC" CMAKE_CXX_OPT_FLAGS)
     if ( CODE_COVERAGE )
         append_cxx_compiler_flags("-g -fprofile-arcs -ftest-coverage -lgcov" "GCC" CMAKE_CXX_FLAGS)

related to gnu c++ default behaviour discussed in, for example, http://freebsd.1045724.x6.nabble.com/base-gcc-and-GLIBCXX-USE-C99-td5781697.html.

sdsl-lite built successfuly in a GNU Guix container this way:

penguin2:~/tmp/sdsl-lite$ ~/opt/guix-guile3/bin/guix environment -C guix --ad-hoc cmake libdivsufsort gcc-toolchain@10.1.0
cmake .
make
(...)
[100%] Linking CXX static library libsdsl_static.a
make[2]: Leaving directory '/home/wrk/tmp/sdsl-lite'
[100%] Built target sdsl_static

Not sure why the gcc-toolchain defaults to this older behaviour on GNU Guix.