有一个非常简单的3文件源代码。
使用cl.exe编译。
- 使用/std:c++17编译时，会出现c++14错误（error C3533: 参数不能具有包含'auto'的类型）。
- 使用/std:c++20编译时，会出现LNK2019。
- 当使用/std:c++20时，并且将
#include <string>从serialization.cpp移动至database.h，则会出现致命的内部编译器错误C1001。
源文件:
database.h:
#pragma once
#include <map>
struct map_manip
{
void operator()(auto& map, uint8_t size = 2);
};
database.cpp:
#include "database.h"
void map_manip::operator()(auto& map, uint8_t size)
{
}
serialization.cpp:
#include "database.h"
#include <string>
struct entry
{
std::map<std::string_view, uint32_t> units;
};
int main()
{
entry x;
map_manip y;
y(x.units);
}
使用c++17编译：
D:\dev\Local\Test>cl /EHsc /std:c++17 serialization.cpp database.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30133 for x86
Copyright (C) Microsoft Corporation. All rights reserved.
serialization.cpp
D:\dev\Local\Test\database.h(8): error C3533: a parameter cannot have a type that contains 'auto'
serialization.cpp(12): error C2664: 'void map_manip::operator ()(unknown-type,uint8_t)': cannot convert argument 1 from 'std::map<std::string_view,uint32_t,std::less<std::string_view>,std::allocator<std::pair<const std::string_view,uint32_t>>>' to 'unknown-type'
D:\dev\Local\Test\database.h(8): note: see declaration of 'map_manip::operator ()'
database.cpp
D:\dev\Local\Test\database.h(8): error C3533: a parameter cannot have a type that contains 'auto'
database.cpp(3): error C3533: a parameter cannot have a type that contains 'auto'
Generating Code...
我相信这些错误在中是有效的，但由于我们使用编译，这不应该是情况。如果我理解错误，请纠正我。
使用c++20编译：
D:\dev\Local\Test>cl /EHsc /std:c++20 serialization.cpp database.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30133 for x86
Copyright (C) Microsoft Corporation. All rights reserved.
serialization.cpp
database.cpp
Generating Code...
Microsoft (R) Incremental Linker Version 14.29.30133.0
Copyright (C) Microsoft Corporation. All rights reserved.
/out:serialization.exe
serialization.obj
database.obj
serialization.obj : error LNK2019: unresolved external symbol "public: void __thiscall map_manip::operator()<class std::map<class std::basic_string_view<char,struct std::char_traits<char> >,unsigned int,struct std::less<class std::basic_string_view<char,struct std::char_traits<char> > >,class std::allocator<struct std::pair<class std::basic_string_view<char,struct std::char_traits<char> > const ,unsigned int> > > >(class std::map<class std::basic_string_view<char,struct std::char_traits<char> >,unsigned int,struct std::less<class std::basic_string_view<char,struct std::char_traits<char> > >,class std::allocator<struct std::pair<class std::basic_string_view<char,struct std::char_traits<char> > const ,unsigned int> > > &,unsigned char)" (??$?RV?$map@V?$basic_string_view@DU?$char_traits@D@std@@@std@@IU?$less@V?$basic_string_view@DU?$char_traits@D@std@@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string_view@DU?$char_traits@D@std@@@std@@I@std@@@2@@std@@@map_manip@@QAEXAAV?$map@V?$basic_string_view@DU?$char_traits@D@std@@@std@@IU?$less@V?$basic_string_view@DU?$char_traits@D@std@@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string_view@DU?$char_traits@D@std@@@std@@I@std@@@2@@std@@E@Z) referenced in function _main
serialization.exe : fatal error LNK1120: 1 unresolved externals
说实话，我完全不理解这个错误，但似乎它与“auto”有些关联。即使将“auto”更改为“template”也没有改变任何事情，但是如果我们从“void operator()”参数中移除“auto& map”（在database.h和database.cpp两个文件中），那么它就可以编译为.exe文件了！
使用c++20编译并将#include <string>从serialization.cpp移到database.h
database.h：
#pragma once
#include <map>
#include <string>
struct map_manip
{
void operator()(auto& map, uint8_t size = 2);
};
serialization.cpp:
#include "database.h"
struct entry
{
std::map<std::string_view, uint32_t> units;
};
int main()
{
entry x;
map_manip y;
y(x.units);
}
在这种情况下，我只会得到一个内部编译器错误。我感觉应该向MSVC开发人员报告此问题，但仍然在此处提供，以防万一。
D:\dev\Local\Test>cl /EHsc /std:c++20 serialization.cpp database.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30133 for x86
Copyright (C) Microsoft Corporation. All rights reserved.
serialization.cpp
serialization.cpp(5): fatal error C1001: Internal compiler error.
(compiler file 'msc1.cpp', line 1603)
To work around this problem, try simplifying or changing the program near the locations listed above.
If possible please provide a repro here: https://developercommunity.visualstudio.com
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
INTERNAL COMPILER ERROR in 'C:\dev\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\bin\HostX86\x86\cl.exe'
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information
非常感谢您的任何想法。