为什么我不能将 gtest ValuesIn 生成器与 std：：map 一起使用？

Why can't I use the gtest ValuesIn generator with a std::map?

本文关键字：map std 一起 不能 gtest ValuesIn 为什么      更新时间：2023-10-16

我正试图用gtest以以下方式对地图的元素运行一些测试：

typedef std::map< std::string, std::vector< std::string > > maptype;
static maptype generateMapOfElements() {...}
class MyTest : public TestWithParam< maptype::value_type > {
...
}
TEST_P(MyTest , my_first_test) { .. }
INSTANTIATE_TEST_CASE_P(test_prefix,
                        MyTest,
                        ValuesIn( generateMapOfElements() ) ); // <- problem

问题似乎是实例化pair::swap会产生问题，因为映射的密钥是常量字符串(下面的完整日志(

1>C:Program Files (x86)Microsoft Visual Studio 11.0VCincludeutility(48): error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const std::string' (or there is no acceptable conversion)
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludexstring(912): could be 'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(std::basic_string<_Elem,_Traits,_Alloc> &&) throw()'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludexstring(969): or       'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(const std::basic_string<_Elem,_Traits,_Alloc> &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludexstring(987): or       'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(const _Elem *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludexstring(992): or       'std::basic_string<_Elem,_Traits,_Alloc> &std::basic_string<_Elem,_Traits,_Alloc>::operator =(_Elem)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          while trying to match the argument list '(const std::string, const std::basic_string<_Elem,_Traits,_Alloc>)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludeutility(56) : see reference to function template instantiation 'void std::swap<_Ty>(_Ty &,_Ty &)' being compiled
1>          with
1>          [
1>              _Ty=std::string
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludeutility(107) : see reference to function template instantiation 'void std::_Swap_adl<_Ty1>(_Ty &,_Ty &)' being compiled
1>          with
1>          [
1>              _Ty1=std::string,
1>              _Ty=std::string
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludeutility(104) : while compiling class template member function 'void std::pair<_Ty1,_Ty2>::swap(std::pair<_Ty1,_Ty2> &)'
1>          with
1>          [
1>              _Ty1=const std::string,
1>              _Ty2=std::vector<testing::internal::string>
1>          ]
1>          C:Program Files (x86)Microsoft Visual Studio 11.0VCincludeutility(211) : see reference to function template instantiation 'void std::pair<_Ty1,_Ty2>::swap(std::pair<_Ty1,_Ty2> &)' being compiled
1>          with
1>          [
1>              _Ty1=const std::string,
1>              _Ty2=std::vector<testing::internal::string>
1>          ]
1>          C:dirmy_test.cpp(251) : see reference to class template instantiation 'std::pair<_Ty1,_Ty2>' being compiled
1>          with
1>          [
1>              _Ty1=const std::string,
1>              _Ty2=std::vector<testing::internal::string>
1>          ]

ValuesIn函数返回一个生成器，该生成器保留值的副本，该副本存储在vector中。(为什么要存储副本？因为通常情况下，它不能依赖原始值源在测试的整个生命周期内保持有效。(vector的要求之一是其元素类型必须是可赋值的(C++03，§23.1/3(。然而，正如您已经注意到的，map::value_type就是pair<const Key, T>。const键类型阻止了该类型的可赋值性。

您可以考虑返回一个vector<pair<string, vector<string>>>，而不是生成器函数中的map<string, vector<string>>。

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