using namespace std;
时间: 2023-11-27 21:46:51 浏览: 31
`using namespace std`是C++中的一个命名空间声明语句,它的作用是将std命名空间中的所有标识符引入当前的命名空间中,从而可以直接使用std命名空间中的函数、变量和类型,而不需要在前面加上std::前缀。例如,如果我们想要使用cout和endl,就可以在程序开头加上`using namespace std`,然后直接使用cout和endl,而不需要写成std::cout和std::endl。
以下是一个使用`using namespace std`的例子:
```c++
#include <iostream>
using namespace std;
int main() {
cout << "Hello, world!" << endl;
return 0;
}
```
输出结果为:
```
Hello, world!
```
相关问题
using namespace std
The "using namespace std" statement in C++ allows you to use all the names in the "std" namespace, which is the namespace for the standard library. This means you can use names like "cout" and "cin" without having to specify the namespace, for example:
```
#include <iostream>
using namespace std;
int main() {
cout << "Hello, world!" << endl;
int x;
cin >> x;
return 0;
}
```
Without the "using namespace std" statement, you would have to qualify the names with the namespace, like this:
```
#include <iostream>
int main() {
std::cout << "Hello, world!" << std::endl;
int x;
std::cin >> x;
return 0;
}
```
While this may not seem like a big deal for a small program like this, it can be very tedious and error-prone for larger programs that use many names from the standard library.