C++打印容器

Question

我正在尝试打印容器，例如集合和 map 。我正在使用的书说以下代码是有效的:

#include <iostream>
#include <set>
#include <iterator>
#include <fstream>
using namespace std;

template <typename Container>
void print (const Container & c, ostream & out = cout)
{
    typename Container::const_iterator itr;
    for( itr=c.begin(); itr!=c.end(); ++itr)
        out << *itr << " ";
    out << endl;
}

int main()
{
    ifstream fin("Test.txt");
    set<string> s(  istream_iterator<string>(fin),
                    istream_iterator<string>() );
    print( s );

    return 0;
}

但是我从 Visual Studio 的编译器收到错误。 我错过了什么？我知道这可能是一些简单的东西，比如包含，但我不熟悉 STL 容器和 C++ 迭代器。

我已经有 #include <iterator>

错误:

• “Container”:后跟“::”时必须是类或命名空间
• 'itr':未声明的标识符
• “const_iterator”:不是“全局命名空间”的成员

我确信还有一些是第一个的结果。

编辑:

根据教科书，以下代码应与我的 main.c 中的代码等效。我无法让它工作，但它可能会有所帮助:

ifstream fin("Test.txt");
string x;
set<string> s;
while( fin >> x)
    s.insert(x);

编辑:

Visual Studio 构建输出:

------ Build started: Project: project, Configuration: Debug Win32 ------
Build started 4/15/2012 1:19:25 PM.
InitializeBuildStatus:

  Touching "Debug\project.unsuccessfulbuild".

ClCompile:

  Project4.cpp

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(11): error C2825: 'Container': must be a class or namespace when followed by '::'

          c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(22) : see reference to function template instantiation 'void print<std::set<_Kty>
(std::istream_iterator<_Ty>,std::istream_iterator<_Ty> (__cdecl *)(void))>(Container (__cdecl &),std::ostream &)' being compiled

          with

          [

              _Kty=std::string,

              _Ty=std::string,

              Container=std::set<std::string> (std::istream_iterator<std::string>,std::istream_iterator<std::string> (__cdecl *)(void))

          ]

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(11): error C2039: 'const_iterator' : is not a member of '`global namespace''

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(11): error C2146: syntax error : missing ';' before identifier 'itr'

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(11): error C2065: 'itr' : undeclared identifier

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(12): error C2065: 'itr' : undeclared identifier

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(12): error C2228: left of '.begin' must have class/struct/union

          type is 'std::set<_Kty> (__cdecl &)'

          with

          [

              _Kty=std::string

          ]

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(12): error C2065: 'itr' : undeclared identifier

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(12): error C2228: left of '.end' must have class/struct/union

          type is 'std::set<_Kty> (__cdecl &)'

          with

          [

              _Kty=std::string

          ]

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(12): error C2065: 'itr' : undeclared identifier

c:\users\admin\documents\visual studio 2010\projects\project\project\project4.cpp(13): error C2065: 'itr' : undeclared identifier



Build FAILED.



Time Elapsed 00:00:01.00

========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

它认为这是一个函数声明:

set<string> s(  istream_iterator<string>(fin),
                istream_iterator<string>() );

添加一对额外的括号可以纠正它:

set<string> s( (istream_iterator<string>(fin)),
                istream_iterator<string>() );

如果您搜索Most Vexing Parse，那么在SO上有很多这样的例子。 .

编辑:您还需要添加 #include <string>