Difference between cout and std::cout in C++
The cout is a predefined object of ostream class, and it is used to print the data on the standard output device. Generally, when we write a program in Linux operating system for G++ compiler, it needs “std” namespace in the program.We use it by writing using namespace std; then we can access any of the objects like cout, cin.
C++
#include <iostream>
int main()
{
std::cout << "GeeksforGeeks" ;
return 0;
}
|
std:cout: A namespace is a declarative region inside which something is defined. So, in that case, cout is defined in the std namespace. Thus, std::cout states that is cout defined in the std namespace otherwise to use the definition of cout which is defined in std namespace. So, that std::cout is used to the definition of cout from std namespace.
C++
#include <iostream>
using namespace std;
int main()
{
cout << "GeeksforGeeks" ;
return 0;
}
|
What would happen if neither “using namespace std” nor “std::” is used for cout?
C++
#include <iostream>
int main()
{
cout << "GeeksforGeeks" ;
return 0;
}
|
Compilation Error:
main.cpp: In function ‘int main()’:
main.cpp:5:2: error:
‘cout’ was not declared in this scope
cout<<"GeeksforGeeks"<<endl;
main.cpp:5:2: note: suggested alternative:
In file included from main.cpp:1:0:
/usr/include/c++/7/iostream:61:18: note: ‘std::cout’
extern ostream cout; /// Linked to standard output
Difference between “using namespace std cout” and “std::cout”?
In C++, cout and std::cout both are same, but there are some basic differences are following:
S. No. |
cout |
std::cout |
1. |
A “namespace std” must be written into the program |
“std::cout” must be used, if “namespace std” was not declared previously |
2. |
cout is a predefined object of the ostream class |
“std::cout” calls the Standard Template/Iostream Library, since “cout” is only defined in the “std” namespace |
3. |
Declaring the namespace before hand gives access to many functions
such as cin, cout etc.
|
This is just an implicit initialization of the std library performed inside the function, i.e alongwith
the main computation
|
Last Updated :
08 Nov, 2022
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