root-project
The implicit `using namespace std;` can have nasty side effects on Windows.
Check duplicate issues.
- [X] Checked for duplicates
Description
As described on the forum trying to '#include <atlstr.h>` in ROOT create a lot of errors:
root [0] #include <atlstr.h>
In file included from ROOT_prompt_0:1:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlstr.h:19:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlbase.h:66:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlcore.h:25:
In file included from C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\Ole2.h:37:
In file included from C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\objbase.h:16:
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h:192:9: error: reference to 'byte' is ambiguous
typedef byte cs_byte;
^
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h:191:23: note: candidate found by name lookup is 'byte'
typedef unsigned char byte;
^
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstddef:28:12: note: candidate found by name lookup is 'std::byte'
enum class byte : unsigned char {};
^
In file included from ROOT_prompt_0:1:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlstr.h:19:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlbase.h:66:
In file included from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\ATLMFC\include\atlcore.h:25:
In file included from C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\Ole2.h:37:
In file included from C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\objbase.h:16:
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h:962:6: error: reference to 'byte' is ambiguous
byte * pNetworkData,
^
[...]
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstddef:28:12: note: candidate found by name lookup is 'std::byte'
enum class byte : unsigned char {};
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
root [1]
To illustrate this, compiling this code:
#include <iostream>
using namespace std;
#include <atlstr.h>
int main() {
std::cout << "hello world!" << std::endl;
return 0;
}
is enough to generate the errors:
C:\Users\bellenot\rootdev>cl -nologo -MD -GR -EHsc -Zc:__cplusplus -std:c++17 atlstr.cxx
atlstr.cxx
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h(192): error C2872: 'byte': ambiguous symbol
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h(191): note: could be 'unsigned char byte'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstddef(28): note: or 'std::byte'
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h(962): error C2872: 'byte': ambiguous symbol
C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\shared\rpcndr.h(191): note: could be 'unsigned char byte'
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstddef(28): note: or 'std::byte'
[...]
And when removing the using namespace std; line, there is no error
Reproducer
On Windows:
root [0] #include <atlstr.h>
ROOT version
Any
Installation method
build from source
Operating system
Windows
Additional context
No response
I thought we got rid of the implicit using namespace std?
I don't know, but that's not good enough anyway (Cling fails too, but with another error) And:
root [1] cout << "hello" << endl;
hello
root [2]
I thought we got rid of the implicit using namespace std?
See https://github.com/root-project/root/blob/master/core/metacling/src/TCling.cxx#L1335-L1336
Yes the PR that removes it is still in Draft mode https://github.com/root-project/root/pull/11027 and needs help.
As a suggestion, if we want to deprecate 'using namespace std' in the long term, we could follow what was being proposed here with 'auto': https://github.com/root-project/root/pull/14645/
Related PR: https://github.com/root-project/root/issues/6411
