Code
2023-11-20 09:00:07

我如何打印出一个向量的内容?

如何将std::vector的内容打印到屏幕上?

实现以下操作符<<的解决方案也很好:

template<container C, class T, String delim = ", ", String open = "[", String close = "]">
std::ostream & operator<<(std::ostream & o, const C<T> & x)
{
  // ... What can I write here?
}

以下是目前为止我所做的，没有单独的函数:

#include <iostream>
#include <fstream>
#include <string>
#include <cmath>
#include <vector>
#include <sstream>
#include <cstdio>
using namespace std;

int main()
{
    ifstream file("maze.txt");
    if (file) {
        vector<char> vec(istreambuf_iterator<char>(file), (istreambuf_iterator<char>()));
        vector<char> path;
        int x = 17;
        char entrance = vec.at(16);
        char firstsquare = vec.at(x);
        if (entrance == 'S') { 
            path.push_back(entrance); 
        }
        for (x = 17; isalpha(firstsquare); x++) {
            path.push_back(firstsquare);
        }
        for (int i = 0; i < path.size(); i++) {
            cout << path[i] << " ";
        }
        cout << endl;
        return 0;
    }
}

当前回答

这已经被编辑了几次，我们决定调用包装集合的主类RangePrinter。

一旦您编写了一次性操作符<< overload，这将自动适用于任何集合，除非您将需要一个特殊的映射来打印对，并且可能希望在那里自定义分隔符。

您还可以在项目上使用特殊的“print”函数，而不是直接输出它，有点像STL算法允许您传入自定义谓词。对于map，您可以这样使用它，使用std::pair的自定义打印机。

您的“默认”打印机只会将其输出到流中。

好的，让我们用一台定制打印机。我将外层类改为RangePrinter。所以我们有两个迭代器和一些分隔符，但还没有定制如何打印实际的项。

struct DefaultPrinter
{
   template< typename T >
   std::ostream & operator()( std::ostream& os, const T& t ) const
   {
     return os << t;
   }

   // overload for std::pair
   template< typename K, typename V >
   std::ostream & operator()( std::ostream & os, std::pair<K,V> const& p)
   {
      return os << p.first << '=' << p.second;
   }
};

// some prototypes
template< typename FwdIter, typename Printer > class RangePrinter;

template< typename FwdIter, typename Printer > 
  std::ostream & operator<<( std::ostream &, 
        RangePrinter<FwdIter, Printer> const& );

template< typename FwdIter, typename Printer=DefaultPrinter >
class RangePrinter
{
    FwdIter begin;
    FwdIter end;
    std::string delim;
    std::string open;
    std::string close;
    Printer printer;

    friend std::ostream& operator<< <>( std::ostream&, 
         RangePrinter<FwdIter,Printer> const& );

public:
    RangePrinter( FwdIter b, FwdIter e, Printer p,
         std::string const& d, std::string const & o, std::string const& c )
      : begin( b ), end( e ), printer( p ), open( o ), close( c )
    {
    } 

     // with no "printer" variable
    RangePrinter( FwdIter b, FwdIter e,
         std::string const& d, std::string const & o, std::string const& c )
      : begin( b ), end( e ), open( o ), close( c )
    {
    } 

};


template<typename FwdIter, typename Printer>
std::ostream& operator<<( std::ostream& os, 
          RangePrinter<FwdIter, Printer> const& range )
{
    const Printer & printer = range.printer;

    os << range.open;
    FwdIter begin = range.begin, end = range.end;

    // print the first item
    if (begin == end) 
    { 
      return os << range.close; 
    }

    printer( os, *begin );

    // print the rest with delim as a prefix
    for( ++begin; begin != end; ++begin )
    {
       os << range.delim;
       printer( os, *begin );
    }
    return os << range.close;
}

现在，默认情况下，只要键和值类型都是可打印的，并且当它们都不是可打印的(就像任何其他类型一样)，或者如果您不想要“=”作为分隔符，它就可以用于映射，并且您可以使用自己的特殊项目打印机。

现在，我将自由函数移到末尾来创建这些:

free-function(迭代器版本)看起来像这样，你甚至可以有默认值:

template<typename Collection>
RangePrinter<typename Collection::const_iterator> rangePrinter
    ( const Collection& coll, const char * delim=",", 
       const char * open="[", const char * close="]")
{
   return RangePrinter< typename Collection::const_iterator >
     ( coll.begin(), coll.end(), delim, open, close );
}

然后你可以将它用于std::set by

 std::cout << outputFormatter( mySet );

您还可以编写带有自定义打印机和带有两个迭代器的自由函数版本。在任何情况下，它们都将为您解析模板参数，并且您将能够将它们作为临时参数传递。

2011-01-31 12:12:18

其他回答

你可以使用std::experimental::make_ostream_joiner:

#include <algorithm>
#include <experimental/iterator>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
 
int main()
{
    std::vector<int> vi(12);
    std::iota(vi.begin(), vi.end(), -5);
    std::cout << "Int vector:\n";
    std::copy(std::begin(vi),
              std::end(vi),
              std::experimental::make_ostream_joiner(std::cout, ", "));

    std::cout <<"\nString vector:\n[";
    std::vector<std::string> vs { "some", "string", "vector" };
    std::copy(std::begin(vs),
              std::end(vs),
              std::experimental::make_ostream_joiner(std::cout, "] - ["));
    std::cout << "]\n";
}

Godbolt演示

2021-06-19 03:07:56

使用std::copy，但没有额外的尾随分隔符

使用std::copy的替代/修改方法(最初在@JoshuaKravtiz answer中使用)，但没有在最后一个元素后面包含额外的尾随分隔符:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

template <typename T>
void print_contents(const std::vector<T>& v, const char * const separator = " ")
{
    if(!v.empty())
    {
        std::copy(v.begin(),
                  --v.end(),
                  std::ostream_iterator<T>(std::cout, separator));
        std::cout << v.back() << "\n";
    }
}

// example usage
int main() {
    std::vector<int> v{1, 2, 3, 4};
    print_contents(v);      // '1 2 3 4'
    print_contents(v, ":"); // '1:2:3:4'
    v = {};
    print_contents(v);      // ... no std::cout
    v = {1};
    print_contents(v);      // '1'
    return 0;
}

用于自定义POD类型容器的示例:

// includes and 'print_contents(...)' as above ...

class Foo
{
    int i;
    friend std::ostream& operator<<(std::ostream& out, const Foo& obj);
public:
    Foo(const int i) : i(i) {}
};

std::ostream& operator<<(std::ostream& out, const Foo& obj)
{
    return out << "foo_" << obj.i; 
}

int main() {
    std::vector<Foo> v{1, 2, 3, 4};
    print_contents(v);      // 'foo_1 foo_2 foo_3 foo_4'
    print_contents(v, ":"); // 'foo_1:foo_2:foo_3:foo_4'
    v = {};
    print_contents(v);      // ... no std::cout
    v = {1};
    print_contents(v);      // 'foo_1'
    return 0;
}
2017-07-30 13:34:54 
template <typename T>
std::ostream& operator<<( std::ostream& ostrm, const std::vector<T>& vec ){
    ostrm << "[";
    for( int j = 0, n = vec.size(); j < n; ++j ){
        ostrm << " " << vec[ j ] << " ,"[ j < n - 1 ];
    }
    return ostrm << "]";
}

[1, 2, 3, 4]

2022-10-11 12:58:24

这是我在2016年完成的实现版本

所有内容都在一个头文件中，所以很容易使用 https://github.com/skident/eos/blob/master/include/eos/io/print.hpp

/*! \file       print.hpp
 *  \brief      Useful functions for work with STL containers. 
 *          
 *  Now it supports generic print for STL containers like: [elem1, elem2, elem3]
 *  Supported STL conrainers: vector, deque, list, set multiset, unordered_set,
 *  map, multimap, unordered_map, array
 *
 *  \author     Skident
 *  \date       02.09.2016
 *  \copyright  Skident Inc.
 */

#pragma once

// check is the C++11 or greater available (special hack for MSVC)
#if (defined(_MSC_VER) && __cplusplus >= 199711L) || __cplusplus >= 201103L
    #define MODERN_CPP_AVAILABLE 1
#endif


#include <iostream>
#include <sstream>
#include <vector>
#include <deque>
#include <set>
#include <list>
#include <map>
#include <cctype>

#ifdef MODERN_CPP_AVAILABLE
    #include <array>
    #include <unordered_set>
    #include <unordered_map>
    #include <forward_list>
#endif


#define dump(value) std::cout << (#value) << ": " << (value) << std::endl

#define BUILD_CONTENT                                                       \
        std::stringstream ss;                                               \
        for (; it != collection.end(); ++it)                                \
        {                                                                   \
            ss << *it << elem_separator;                                    \
        }                                                                   \


#define BUILD_MAP_CONTENT                                                   \
        std::stringstream ss;                                               \
        for (; it != collection.end(); ++it)                                \
        {                                                                   \
            ss  << it->first                                                \
                << keyval_separator                                         \
                << it->second                                               \
                << elem_separator;                                          \
        }                                                                   \


#define COMPILE_CONTENT                                                     \
        std::string data = ss.str();                                        \
        if (!data.empty() && !elem_separator.empty())                       \
            data = data.substr(0, data.rfind(elem_separator));              \
        std::string result = first_bracket + data + last_bracket;           \
        os << result;                                                       \
        if (needEndl)                                                       \
            os << std::endl;                                                \



////
///
///
/// Template definitions
///
///

//generic template for classes: deque, list, forward_list, vector
#define VECTOR_AND_CO_TEMPLATE                                          \
    template<                                                           \
        template<class T,                                               \
                 class Alloc = std::allocator<T> >                      \
        class Container, class Type, class Alloc>                       \

#define SET_TEMPLATE                                                    \
    template<                                                           \
        template<class T,                                               \
                 class Compare = std::less<T>,                          \
                 class Alloc = std::allocator<T> >                      \
            class Container, class T, class Compare, class Alloc>       \

#define USET_TEMPLATE                                                   \
    template<                                                           \
template < class Key,                                                   \
           class Hash = std::hash<Key>,                                 \
           class Pred = std::equal_to<Key>,                             \
           class Alloc = std::allocator<Key>                            \
           >                                                            \
    class Container, class Key, class Hash, class Pred, class Alloc     \
    >                                                                   \


#define MAP_TEMPLATE                                                    \
    template<                                                           \
        template<class Key,                                             \
                class T,                                                \
                class Compare = std::less<Key>,                         \
                class Alloc = std::allocator<std::pair<const Key,T> >   \
                >                                                       \
        class Container, class Key,                                     \
        class Value/*, class Compare, class Alloc*/>                    \


#define UMAP_TEMPLATE                                                   \
    template<                                                           \
        template<class Key,                                             \
                   class T,                                             \
                   class Hash = std::hash<Key>,                         \
                   class Pred = std::equal_to<Key>,                     \
                   class Alloc = std::allocator<std::pair<const Key,T> >\
                 >                                                      \
        class Container, class Key, class Value,                        \
        class Hash, class Pred, class Alloc                             \
                >                                                       \


#define ARRAY_TEMPLATE                                                  \
    template<                                                           \
        template<class T, std::size_t N>                                \
        class Array, class Type, std::size_t Size>                      \



namespace eos
{
    static const std::string default_elem_separator     = ", ";
    static const std::string default_keyval_separator   = " => ";
    static const std::string default_first_bracket      = "[";
    static const std::string default_last_bracket       = "]";


    //! Prints template Container<T> as in Python
    //! Supported containers: vector, deque, list, set, unordered_set(C++11), forward_list(C++11)
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    template<class Container>
    void print( const Container& collection
              , const std::string& elem_separator   = default_elem_separator
              , const std::string& first_bracket    = default_first_bracket
              , const std::string& last_bracket     = default_last_bracket
              , std::ostream& os = std::cout
              , bool needEndl = true
            )
    {
        typename Container::const_iterator it = collection.begin();
        BUILD_CONTENT
        COMPILE_CONTENT
    }


    //! Prints collections with one template argument and allocator as in Python.
    //! Supported standard collections: vector, deque, list, forward_list
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    VECTOR_AND_CO_TEMPLATE
    void print( const Container<Type>& collection
              , const std::string& elem_separator   = default_elem_separator
              , const std::string& first_bracket    = default_first_bracket
              , const std::string& last_bracket     = default_last_bracket
              , std::ostream& os = std::cout
              , bool needEndl = true
            )
    {
        typename Container<Type>::const_iterator it = collection.begin();
        BUILD_CONTENT
        COMPILE_CONTENT
    }


    //! Prints collections like std:set<T, Compare, Alloc> as in Python
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    SET_TEMPLATE
    void print( const Container<T, Compare, Alloc>& collection
              , const std::string& elem_separator   = default_elem_separator
              , const std::string& first_bracket    = default_first_bracket
              , const std::string& last_bracket     = default_last_bracket
              , std::ostream& os = std::cout
              , bool needEndl = true
            )
    {
        typename Container<T, Compare, Alloc>::const_iterator it = collection.begin();
        BUILD_CONTENT
        COMPILE_CONTENT
    }


    //! Prints collections like std:unordered_set<Key, Hash, Pred, Alloc> as in Python
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    USET_TEMPLATE
    void print( const Container<Key, Hash, Pred, Alloc>& collection
              , const std::string& elem_separator   = default_elem_separator
              , const std::string& first_bracket    = default_first_bracket
              , const std::string& last_bracket     = default_last_bracket
              , std::ostream& os = std::cout
              , bool needEndl = true
            )
    {
        typename Container<Key, Hash, Pred, Alloc>::const_iterator it = collection.begin();
        BUILD_CONTENT
        COMPILE_CONTENT
    }

    //! Prints collections like std:map<T, U> as in Python
    //! supports generic objects of std: map, multimap
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    MAP_TEMPLATE
    void print(   const Container<Key, Value>& collection
                , const std::string& elem_separator   = default_elem_separator
                , const std::string& keyval_separator = default_keyval_separator
                , const std::string& first_bracket    = default_first_bracket
                , const std::string& last_bracket     = default_last_bracket
                , std::ostream& os = std::cout
                , bool needEndl = true
        )
    {
        typename Container<Key, Value>::const_iterator it = collection.begin();
        BUILD_MAP_CONTENT
        COMPILE_CONTENT
    }

    //! Prints classes like std:unordered_map as in Python
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    UMAP_TEMPLATE
    void print(   const Container<Key, Value, Hash, Pred, Alloc>& collection
                , const std::string& elem_separator   = default_elem_separator
                , const std::string& keyval_separator = default_keyval_separator
                , const std::string& first_bracket    = default_first_bracket
                , const std::string& last_bracket     = default_last_bracket
                , std::ostream& os = std::cout
                , bool needEndl = true
        )
    {
        typename Container<Key, Value, Hash, Pred, Alloc>::const_iterator it = collection.begin();
        BUILD_MAP_CONTENT
        COMPILE_CONTENT
    }

    //! Prints collections like std:array<T, Size> as in Python
    //! \param collection which should be printed
    //! \param elem_separator the separator which will be inserted between elements of collection
    //! \param keyval_separator separator between key and value of map. For default it is the '=>'
    //! \param first_bracket data before collection's elements (usual it is the parenthesis, square or curly bracker '(', '[', '{')
    //! \param last_bracket data after collection's elements (usual it is the parenthesis, square or curly bracker ')', ']', '}')
    ARRAY_TEMPLATE
    void print(   const Array<Type, Size>& collection
                , const std::string& elem_separator   = default_elem_separator
                , const std::string& first_bracket    = default_first_bracket
                , const std::string& last_bracket     = default_last_bracket
                , std::ostream& os = std::cout
                , bool needEndl = true
            )
    {
        typename Array<Type, Size>::const_iterator it = collection.begin();
        BUILD_CONTENT
        COMPILE_CONTENT
    }

    //! Removes all whitespaces before data in string.
    //! \param str string with data
    //! \return string without whitespaces in left part
    std::string ltrim(const std::string& str);

    //! Removes all whitespaces after data in string
    //! \param str string with data
    //! \return string without whitespaces in right part
    std::string rtrim(const std::string& str);

    //! Removes all whitespaces before and after data in string
    //! \param str string with data
    //! \return string without whitespaces before and after data in string
    std::string trim(const std::string& str);



    ////////////////////////////////////////////////////////////
    ////////////////////////ostream logic//////////////////////
    /// Should be specified for concrete containers
    /// because of another types can be suitable
    /// for templates, for example templates break
    /// the code like this "cout << string("hello") << endl;"
    ////////////////////////////////////////////////////////////



#define PROCESS_VALUE_COLLECTION(os, collection)                            \
    print(  collection,                                                     \
            default_elem_separator,                                         \
            default_first_bracket,                                          \
            default_last_bracket,                                           \
            os,                                                             \
            false                                                           \
    );                                                                      \

#define PROCESS_KEY_VALUE_COLLECTION(os, collection)                        \
    print(  collection,                                                     \
            default_elem_separator,                                         \
            default_keyval_separator,                                       \
            default_first_bracket,                                          \
            default_last_bracket,                                           \
            os,                                                             \
            false                                                           \
    );                                                                      \

    ///< specialization for vector
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::vector<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for deque
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::deque<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for list
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::list<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for set
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::set<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for multiset
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::multiset<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

#ifdef MODERN_CPP_AVAILABLE
    ///< specialization for unordered_map
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::unordered_set<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for forward_list
    template<class T>
    std::ostream& operator<<(std::ostream& os, const std::forward_list<T>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for array
    template<class T, std::size_t N>
    std::ostream& operator<<(std::ostream& os, const std::array<T, N>& collection)
    {
        PROCESS_VALUE_COLLECTION(os, collection)
        return os;
    }
#endif

    ///< specialization for map, multimap
    MAP_TEMPLATE
    std::ostream& operator<<(std::ostream& os, const Container<Key, Value>& collection)
    {
        PROCESS_KEY_VALUE_COLLECTION(os, collection)
        return os;
    }

    ///< specialization for unordered_map
    UMAP_TEMPLATE
    std::ostream& operator<<(std::ostream& os, const Container<Key, Value, Hash, Pred, Alloc>& collection)
    {
        PROCESS_KEY_VALUE_COLLECTION(os, collection)
        return os;
    }
}
2020-05-24 06:06:20

这里是一个工作库，作为一个完整的工作程序，我刚刚把它组合在一起:

#include <set>
#include <vector>
#include <iostream>

#include <boost/utility/enable_if.hpp>

// Default delimiters
template <class C> struct Delims { static const char *delim[3]; };
template <class C> const char *Delims<C>::delim[3]={"[", ", ", "]"};
// Special delimiters for sets.                                                                                                             
template <typename T> struct Delims< std::set<T> > { static const char *delim[3]; };
template <typename T> const char *Delims< std::set<T> >::delim[3]={"{", ", ", "}"};

template <class C> struct IsContainer { enum { value = false }; };
template <typename T> struct IsContainer< std::vector<T> > { enum { value = true }; };
template <typename T> struct IsContainer< std::set<T>    > { enum { value = true }; };

template <class C>
typename boost::enable_if<IsContainer<C>, std::ostream&>::type
operator<<(std::ostream & o, const C & x)
{
  o << Delims<C>::delim[0];
  for (typename C::const_iterator i = x.begin(); i != x.end(); ++i)
    {
      if (i != x.begin()) o << Delims<C>::delim[1];
      o << *i;
    }
  o << Delims<C>::delim[2];
  return o;
}

template <typename T> struct IsChar { enum { value = false }; };
template <> struct IsChar<char> { enum { value = true }; };

template <typename T, int N>
typename boost::disable_if<IsChar<T>, std::ostream&>::type
operator<<(std::ostream & o, const T (&x)[N])
{
  o << "[";
  for (int i = 0; i != N; ++i)
    {
      if (i) o << ",";
      o << x[i];
    }
  o << "]";
  return o;
}

int main()
{
  std::vector<int> i;
  i.push_back(23);
  i.push_back(34);

  std::set<std::string> j;
  j.insert("hello");
  j.insert("world");

  double k[] = { 1.1, 2.2, M_PI, -1.0/123.0 };

  std::cout << i << "\n" << j << "\n" << k << "\n";
}

它目前只适用于vector和set，但通过扩展IsContainer专门化，可以使其适用于大多数容器。我没有过多地考虑这些代码是否最少，但我不能立即想到任何可以去掉的冗余代码。

编辑:只是为了好玩，我包含了一个处理数组的版本。我不得不排除字符数组，以避免进一步的歧义;使用wchar_t[]仍然会遇到麻烦。

2011-01-31 11:51:51

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