configure: error: cannot figure out how to use std::filesystem #27148

Got this error from configure when trying to build from tag v24.0.1 on Ubuntu 18.

At first my gcc was version gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) so I tried installing clang 10: clang version 10.0.0-4ubuntu1~18.04.2 and linked to CXX, etc... still got the same error.

$ uname -a
Linux party 4.15.0-163-generic [#171](/bitcoin-bitcoin/171/)-Ubuntu SMP Fri Nov 5 11:55:11 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.4 LTS
Release:        18.04
Codename:       bionic

Complete output:

$ ./configure --without-gui --with-incompatible-bdb
checking for pkg-config... /usr/bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking whether to enable maintainer-specific portions of Makefiles... yes
checking whether make supports nested variables... (cached) yes
checking whether the C++ compiler works... yes
checking for C++ compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C++ compiler... yes
checking whether /usr/bin/clang++-10 accepts -g... yes
checking for style of include used by make... GNU
checking dependency style of /usr/bin/clang++-10... gcc3
checking whether /usr/bin/clang++-10 supports C++17 features with -std=c++17... yes
checking whether std::filesystem can be used without link library... no
checking whether std::filesystem needs -lstdc++fs... no
checking whether std::filesystem needs -lc++fs... configure: error: in `/root/bitcoin':
configure: error: cannot figure out how to use std::filesystem
See `config.log' for more details

./configure --without-gui --with-incompatible-bdb

I see clang is being used in the output, but how are you passing clang through? CC=clang=10 CXX=clang++? What is the actual output in config.log?

yeah:

$ env | grep clang
CC=/usr/bin/clang-10
CXX=/usr/bin/clang++-10

This is the relevant chunk from config.log:

configure:4823: checking whether /usr/bin/clang++-10 supports C++17 features with -std=c++17
configure:5619: /usr/bin/clang++-10 -std=c++17 -c -g -O2  conftest.cpp >&5
configure:5619: $? = 0
configure:5628: result: yes
configure:6565: checking whether std::filesystem can be used without link library
configure:6581: /usr/bin/clang++-10 -std=c++17 -o conftest -g -O2   conftest.cpp  >&5
conftest.cpp:11:12: fatal error: 'filesystem' file not found
  #include <filesystem>
           ^~~~~~~~~~~~
1 error generated.
configure:6581: $? = 1
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME "Bitcoin Core"
| #define PACKAGE_TARNAME "bitcoin"
| #define PACKAGE_VERSION "24.0.1"
| #define PACKAGE_STRING "Bitcoin Core 24.0.1"
| #define PACKAGE_BUGREPORT "https://github.com/bitcoin/bitcoin/issues"
| #define PACKAGE_URL "https://bitcoincore.org/"
| #define HAVE_CXX17 1
| /* end confdefs.h.  */
|
|   #include <filesystem>
|
|   namespace fs = std::filesystem;
|
|   int main() {
|     (void)fs::current_path().root_name();
|     return 0;
|   }
|
configure:6588: result: no
configure:6592: checking whether std::filesystem needs -lstdc++fs
configure:6607: /usr/bin/clang++-10 -std=c++17 -o conftest -g -O2   conftest.cpp  -lstdc++fs >&5
conftest.cpp:11:12: fatal error: 'filesystem' file not found
  #include <filesystem>
           ^~~~~~~~~~~~
1 error generated.
configure:6607: $? = 1
configure: failed program was:
| /* confdefs.h */
| #define PACKAGE_NAME "Bitcoin Core"
| #define PACKAGE_TARNAME "bitcoin"
| #define PACKAGE_VERSION "24.0.1"
| #define PACKAGE_STRING "Bitcoin Core 24.0.1"
| #define PACKAGE_BUGREPORT "https://github.com/bitcoin/bitcoin/issues"
| #define PACKAGE_URL "https://bitcoincore.org/"
| #define HAVE_CXX17 1
| /* end confdefs.h.  */
|
|   #include <filesystem>
|
|   namespace fs = std::filesystem;
|
|   int main() {
|     (void)fs::current_path().root_name();
|     return 0;
|   }
configure:6614: result: no
configure:6616: checking whether std::filesystem needs -lc++fs
configure:6632: /usr/bin/clang++-10 -std=c++17 -o conftest -g -O2   conftest.cpp  -lc++fs >&5
conftest.cpp:11:12: fatal error: 'filesystem' file not found
  #include <filesystem>
           ^~~~~~~~~~~~

Errors in config.log look the same with gcc 7 too:

checking whether g++ supports C++17 features with -std=c++17... yes
checking whether std::filesystem can be used without link library... no
checking whether std::filesystem needs -lstdc++fs... no
checking whether std::filesystem needs -lc++fs... configure: error: in `/root/bitcoin':
configure: error: cannot figure out how to use std::filesystem
See `config.log' for more details

yeah:

$ env | grep clang
CC=/usr/bin/clang-10
CXX=/usr/bin/clang++-10

You're still using an old libstdc++.

gcc 7 doesn't have filesystem. You can try CC=clang-10 CXX="clang++-10 -stdlib=libc++"

This is the relevant chunk from config.log:

Installing libstdc++-8-dev will solve the problem.

Installing libstdc++-8-dev will solve the problem.

YES! Thanks. Add to docs ?

Add to docs ?

Probably, it does not worth, considering that Ubuntu 18 is about to reach "End of Standard Support" soon.

See also https://github.com/bitcoin/bitcoin/blob/master/doc/dependencies.md#dependencies:

• #24164
• https://github.com/bitcoin/bitcoin/pull/23060

This is the relevant chunk from config.log:

Installing libstdc++-8-dev will solve the problem.

how to install this lib？

@wangtao19911111 The minimum required version is installed by default with g++, if you use the latest LTS release of your operating system.