取消引用字符串迭代器将无法编译

Question

I have a problem where example code will compile and run in the Code Blocks environment but will not compile in visual studio 2012

list<string> names;
names.push_back("Mary");
names.push_back("Zach");
names.push_back("Elizabeth");
list<string>::iterator iter = names.begin();
while (iter != names.end()) {
    cout << *iter << endl;  // This dereference causes compile error C2679
    ++iter;
}

Results in the following compiler error

1>chapter_a0602.cpp(20): error C2679: binary '<<' : no operator found which takes a
right-hand operand of type 'std::basic_string<_Elem,_Traits,_Alloc>' (or there is no
acceptable conversion)
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Alloc=std::allocator<char>
1>          ]

when I change the list of strings to a list of ints the code compiles and runs in VS2012.

when I also change the dereference to the following it compiles

cout << *the_iter->c_str() << endl;

However I have two other dereference problems further down the code

cout << "first item: " << names.front() << endl;
cout << "last item: "  << names.back() << endl;

I really don't understand why these errors are compiler dependant.

sorry about the formatting but I couldn't get it to accept the code.

Answer 1

Add the following include directive:

#include <string>

as that is where operator<<(std::ostream&, std::string&) is defined.

Note VS2012 supports the range-based for statement , which would transform the outputting loop to:

for (auto const& name: names) std::cout << name << std::endl;

Answer 2

The ostream operator<<(ostream& os, const string& str) is defined in the string header.

You probably just forgot to include it to have this kind of error.

You should just include it at the top of your file :

#include <string>

Live example .