c++ - 我怎样才能允许将 vector 传递给 INFO()、CAPTURE()、WARN() 等，同时避免非法扩展 std namespace ？

Question

在 Catch Unit Test v1.8.1 中，使用 gcc 6.2.0，我试图在测试失败时通过将 vector 传递给 INFO(...) 来方便地输出 vector 的内容。或 CAPTURE(...) .为此，我重载了流插入运算符:

#include <Catch/single_include/catch.hpp>
#include <vector>
#include <iostream>

#define THIS_WORKS_BUT_EXTENDING_NAMESPACE_STD_IS_ILLEGAL
#ifdef THIS_WORKS_BUT_EXTENDING_NAMESPACE_STD_IS_ILLEGAL
namespace std {
#endif

std::ostream& operator<<( std::ostream& os, const std::vector<int>& v ) {
    for ( const auto& e : v ) {
        os << e << " ";
    }
    return os;
}

#ifdef THIS_WORKS_BUT_EXTENDING_NAMESPACE_STD_IS_ILLEGAL
} //namespace std
#endif

int some_operation_on_vector( const std::vector<int>& v ) {
    return 1;
}

SCENARIO( "some scenario" )
{
    GIVEN( "a vector" )
    {
        const auto the_vector = std::vector<int>{ 1, 2, 3, 4, 5 };

        WHEN( "some result is calculated from the vector" )
        {
            const auto actual_result = some_operation_on_vector( the_vector );

            THEN( "the result should be correct.  If not, print out the vector." )
            {
                const auto expected_result = 0;

                CAPTURE( the_vector ); // <--------
                //^^^^
                //How do I legally make this work?

                REQUIRE( expected_result == actual_result );
            }
        }
    }
}

---

如果我(非法)扩展 std namespace 如上，然后它可以工作，我看到了所需的输出:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
catchtestexample is a Catch v1.8.1 host application.
Run with -? for options

-------------------------------------------------------------------------------
Scenario: some scenario
     Given: a vector
      When: some result is calculated from the vector
      Then: the result should be correct.  If not, print out the vector.
-------------------------------------------------------------------------------
ExampleTest.cpp:91
...............................................................................

ExampleTest.cpp:95: FAILED:
  REQUIRE( expected_result == actual_result )
with expansion:
  0 == 1
with message:
  the_vector := 1 2 3 4 5 

===============================================================================
test cases: 1 | 1 failed
assertions: 1 | 1 failed

但是为了合法，当我尝试移动 operator<<重载 std命名空间并进入全局命名空间(通过注释掉 #define THIS_WORKS_BUT_EXTENDING_NAMESPACE_STD_IS_ILLEGAL )，由于将 vector 传递给 CAPTURE()，代码无法编译宏。

根据 Catch docs ，我尝试更换 operator <<用 Catch::toString 重载过载:

#include <string>
#include <sstream>

namespace Catch {
    std::string toString( const std::vector<int>& v ) {
        std::ostringstream ss;
        for ( const auto& e : v ) {
            ss << e << " ";
        }
        return ss.str();
    }
}

或使用 Catch::StringMaker专业:

#include <string>
#include <sstream>

namespace Catch {
    template<> struct StringMaker<std::vector<int>> {
        static std::string convert( const std::vector<int>& v ) {
            std::ostringstream ss;
            for ( const auto& e : v ) {
                ss << e << " ";
            }
            return ss.str();
        }
    }; 
}

但在任何一种情况下，由于将 vector 传递给 CAPTURE()，测试仍然无法编译。宏。

Catch 文档说要放置 operator<<重载到与您的类型相同的命名空间，但是 std::vector不是我的类型，并将该重载放入命名空间 std是非法的。

但我找到的唯一方法是 CAPTURE() (或 INFO() 或 WARN() 等)接受 std::vector参数是非法放置 operator<<重载到命名空间 std .

是否有适当、合法的方式来做到这一点？

Answer 1

我想我找到了一个有效的答案。 (编辑:请参阅 other answer 以获得更好的解决方案。)

而不是把 operator<<重载到 std命名空间，将其放入 Catch命名空间编译并给出所需的行为:

namespace Catch {

std::ostream& operator<<( std::ostream& os, const std::vector<int>& v ) {
    for ( const auto& e : v ) {
        os << e << " ";
    }
    return os;
}

}

Catch docs说把operator<<重载到与您的类型相同的 namespace 中:

operator<< overload for std::ostream

This is the standard way of providing string conversions in C++ - and the chances are you may already provide this for your own purposes. If you're not familiar with this idiom it involves writing a free function of the form:

   std::ostream& operator<<( std::ostream& os, T const& value ) {
       os << convertMyTypeToString( value );
       return os;
   }

(where T is your type and convertMyTypeToString is where you'll write whatever code is necessary to make your type printable - it doesn't have to be in another function).

You should put this function in the same namespace as your type. [Emphasis mine]

Alternatively you may prefer to write it as a member function:

   std::ostream& T::operator<<( std::ostream& os ) const {
       os << convertMyTypeToString( *this );
       return os;
   }

但是因为 std::vector 不是我的类型，它位于命名空间 std 中，我无法按照文档所说的去做。

所以可以把operator<<重载到 Catch命名空间代替？它有效，但是可以吗？如果我这样做会发生坏事吗？文档确实说可以重载 toString进入 Catch 命名空间，所以这对 operator<< 没问题吗？也有过载？