在linux下编译模板程序出错，出错信息如下,而同样的代码在vs2003中编译通过，google了一下原来是使用vector<T>内部类型iterator时需要添加typename，加上typename后编译通过。

meta:/var/ftp/upload/test # g++ -o temp template.cpp
template.cpp: In function ‘std::string print(std::vector<Type, std::allocator<_CharT> >)’:
template.cpp:16: error: expected `;' before ‘it’
template.cpp:17: error: ‘it’ was not declared in this scope
template.cpp: In function ‘std::string print(std::vector<Type, std::allocator<_CharT> >) [with Type = int]’:
template.cpp:29:   instantiated from here
template.cpp:16: error: dependent-name ‘std::vector<Type,std::allocator<_CharT> >::iterator’ is parsed as a non-type, but instantiation yields a type
template.cpp:16: note: say ‘typename std::vector<Type,std::allocator<_CharT> >::iterator’ if a type is meant
代码如下：

//template.cpp

#include<iostream>
#include<vector>
#include<string>
#include<sstream>

using namespace std; 

template<class Type>
string print(vector<Type> vt)
{
 stringstream ss;
 for(vector<Type>::iterator it = vt.begin(); it < vt.end(); it++)
 {
  ss << *it << " " << endl;
 }
 return ss.str();
}

int main()
{
 vector<int> vi;
 vi.push_back(100);
 vi.push_back(123);
 string str = print(vi);
 cout << str;
 return 0;
}

typename两种用法：

1。用在模板声明中，如下两个声明是一样的：

template<class T> class Widget; // uses "class"
template<typename T> class Widget; // uses "typename"

2.用于标识 nested dependent type name（嵌套依赖类型名）