C++ 为什么我不能cout一个字符串？
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Why I cannot cout a string?
提问by Ata
Why I cannot coutstringlike this:
为什么我不coutstring喜欢这个：
string text ;
text = WordList[i].substr(0,20) ;
cout << "String is : " << text << endl ;
When I do this, I get the following error:
当我这样做时，我收到以下错误：
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**
错误 2 错误 C2679：二进制“<<”：未找到采用“std::string”类型的右侧操作数的运算符（或没有可接受的转换） c:\users\mollasadra\documents\visual studio 2008\项目\barnamec\barnamec\barnamec.cpp 67 barnamec**
It is amazing, that even this is not working:
令人惊讶的是，即使这样也行不通：
string text ;
text = "hello" ;
cout << "String is : " << text << endl ;
回答by Kiril Kirov
You need to include
你需要包括
#include <string>
#include <iostream>
回答by nperson325681
You need to reference the cout's namespace stdsomehow. For instance, insert
您需要以std某种方式引用 cout 的命名空间。例如，插入
using std::cout;
using std::endl;
on top of your function definition, or the file.
在您的函数定义或文件之上。
回答by sepp2k
There are several problems with your code:
您的代码有几个问题：
WordListis not defined anywhere. You should define it before you use it.- You can't just write code outside a function like this. You need to put it in a function.
- You need to
#include <string>before you can use the string class and iostream before you usecoutorendl. string,coutandendllive in thestdnamespace, so you can not access them without prefixing them withstd::unless you use theusingdirective to bring them into scope first.
WordList没有在任何地方定义。你应该在使用它之前定义它。- 你不能只是在这样的函数之外编写代码。你需要把它放在一个函数中。
#include <string>在使用coutor之前，您需要先使用字符串类和 iostreamendl。string,cout并且endl位于std命名空间中，因此std::除非您先使用using指令将它们引入作用域，否则您无法在不使用前缀的情况下访问它们。
回答by Maheswar Reddy
Above answers are good but If you do not want to add string include, you can use the following
上面的答案很好，但如果你不想添加字符串包含，你可以使用以下
ostream& operator<<(ostream& os, string& msg)
{
os<<msg.c_str();
return os;
}
回答by Anthony.
Use c_str() to convert the std::string to const char *.
使用 c_str() 将 std::string 转换为 const char *。
cout << "String is : " << text.c_str() << endl ;
回答by Ash Ghal
You do not have to reference std::coutor std::endlexplicitly.
They are both included in the namespace std. using namespace stdinstead of using scope resolution operator ::every time makes is easier and cleaner.
您不必引用std::cout或std::endl明确。
它们都包含在namespace std. using namespace std而不是::每次都使用范围解析运算符，这样更容易和更清晰。
#include<iostream>
#include<string>
using namespace std;
回答by pratikpchpr
If you are using linux system then you need to add
如果你使用的是linux系统，那么你需要添加
using namespace std;
using namespace std;
Below headers
标题下方
If windows then make sure you put headers correctly
#include<iostream.h>
如果 Windows 则确保正确放置标题
#include<iostream.h>
#include<string.h>
#include<string.h>
Refer this it work perfectly.
参考这个它完美地工作。
#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;
}
