如何在CppUnit中漂亮地打印STL數據結構？

Question

我想漂亮打印STL數據結構與下面的代碼

#include <iostream> 
#include <utility> 
#include <map> 
#include <sstream> 
template<class S,class T> 
std::ostream& operator<<(std::ostream & o, const std::pair<S,T> & p){ 
     return o << "(" << p.first << ", " << p.second << ")"; 
} 

template<class K, class V> 
std::ostream& operator<<(std::ostream& o, const std::map<K,V> & m){ 
    o << "{ "; 
    for(auto it=m.begin();it!=m.end();it++){ 
     o << "{" << it->first <<": " << it->second << "} "; 
    } 
    o << " }"; 
    return o; 
}  

但是，當我用這包括在一些測試文件中像

auto a = std::map<int,int>(); 
auto b = std::map<int,int>(); 
CPPUNIT_ASSERT_EQUAL(a,b); 

我得到的視察CppUnit的測試結果以下錯誤：

In file included from /usr/include/cppunit/TestCase.h:6:0, 
       from /usr/include/cppunit/TestCaller.h:5, 
       from /usr/include/cppunit/extensions/HelperMacros.h:9, 
       from /home/tcebrian/GIT/compress-sn/test/GraphTest.cpp:1: 
/usr/include/cppunit/TestAssert.h: In static member function 'static std::string CppUnit::assertion_traits<T>::toString(const T&) [with T = std::map<int, int>, std::string = std::basic_string<char>]': 
/usr/include/cppunit/TestAssert.h:101:5: instantiated from 'void CppUnit::assertEquals(const T&, const T&, CppUnit::SourceLine, const string&) [with T = std::map<int, int>, std::string = std::basic_string<char>]' 
/home/tcebrian/GIT/compress-sn/test/GraphTest.cpp:44:9: instantiated from here 
/usr/include/cppunit/TestAssert.h:49:9: error: cannot bind 'std::basic_ostream<char>' lvalue to 'std::basic_ostream<char>&&' 
/usr/include/c++/4.6/ostream:581:5: error: initializing argument 1 of 'std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT = char, _Traits = std::char_traits<char>, _Tp = std::map<int, int>]' 
make[3]: *** [CMakeFiles/UnitTester.dir/test/GraphTest.cpp.o] Error 1 
make[3]: Leaving directory `/home/tcebrian/GIT/compress-sn/dist/Debug' 
make[2]: *** [CMakeFiles/UnitTester.dir/all] Error 2 
make[2]: Leaving directory `/home/tcebrian/GIT/compress-sn/dist/Debug' 
make[1]: *** [all] Error 2 
make[1]: Leaving directory `/home/tcebrian/GIT/compress-sn/dist/Debug' 
make: *** [debug] Error 2 

但該代碼是在這個簡單的片斷完全合法：

#include <TestUtils.hpp> 
#include <map> 
#include <utility> 
int main(int argc, const char *argv[]) 
{ 
    std::cout << std::pair<int,int>() << std::endl; 
    std::cout << std::map<int,int>() << std::endl; 
    return 0; 
} 

什麼是CppUnit這樣做可以防止漂亮的打印數據結構？你如何用CppUnit打印？

Answer 1

我不知道爲什麼你會得到那個特定的錯誤（不知何故，它認爲他們使用< <運算符被定義爲採用右值引用std :: ostream），但它看起來像推薦的方式可能是專門化了CppUnit :: assertion_traits模板，如TestAssert.h所示。就像這樣：

namespace CppUnit{ 
    template<class X, class Y> 
    struct assertion_traits<std::pair<X,Y>>{ 
     static bool equal(const std::pair<X,Y> &a, const std::pair<X,Y> &b){ 
      return a == b; 
     } 
     static std::string toString(const std::pair<X,Y> &p){ 
      std::ostringstream o; 
      o << "(" << p.first << ", " << p.second << ")"; 
      return o.str(); 
     } 
    }; 
}