为什么我不能找到一个字符串？

Question

Why I cannot cout string like this:

string text ;
text = WordList[i].substr(0,20) ;
cout << "String is  : " << text << endl ;

When I do this, I get the following error:

Error 2 error C2679: binary '<<': no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion) c:\users\mollasadra\documents\visual studio 2008\projects\barnamec\barnamec\barnamec.cpp 67 barnamec**

It is amazing, that even this is not working:

string text ;
text = "hello"  ;
cout << "String is  : " << text << endl ;

Answer 1

You need to include

#include <string>
#include <iostream>

Answer 2

You need to reference the cout's namespace std somehow. For instance, insert

using std::cout;
using std::endl;

on top of your function definition, or the file.

Answer 3

There are several problems with your code:

1. WordList is not defined anywhere. You should define it before you use it.
2. You can't just write code outside a function like this. You need to put it in a function.
3. You need to #include <string> before you can use the string class and iostream before you use cout or endl .
4. string , cout and endl live in the std namespace, so you can not access them without prefixing them with std:: unless you use the using directive to bring them into scope first.

Answer 4

Above answers are good but If you do not want to add string include, you can use the following

ostream& operator<<(ostream& os, string& msg)
{
os<<msg.c_str();

return os;
}

Answer 5

Use c_str() to convert the std::string to const char *.

cout << "String is  : " << text.c_str() << endl ;

Answer 6

You do not have to reference std::cout or std::endl explicitly.
They are both included in the namespace std . using namespace std instead of using scope resolution operator :: every time makes is easier and cleaner.

#include<iostream>
#include<string>
using namespace std;

Answer 7

If you are using linux system then you need to add

using namespace std;

Below headers

If windows then make sure you put headers correctly #include<iostream.h>

#include<string.h>

Refer this it work perfectly.

#include <iostream>
#include <string>

int main ()
{
std::string str="We think in generalities, but we live in details.";
                                       // (quoting Alfred N. Whitehead)

  std::string str2 = str.substr (3,5);     // "think"

   std::size_t pos = str.find("live");      // position of "live" in str

  std::string str3 = str.substr (pos);     
// get from "live" to the end

  std::cout << str2 << ' ' << str3 << '\n';

  return 0;
}