c++ identifier is undefined [SOLVED]

If you are new to c++ programming language then possibly you will come across c++ identifier is undefined errors. You might get identifier is undefined error in multiple ways, below 4 different possible errors for identifier is undefined in c++.

Possible different errors:

1. c++ identifier is undefined
2. c++ identifier cout is undefined
3. c++ identifier string is undefined
4. identifier system is undefined c++
   

1) c++ identifier is undefined

Solution-1 : identifier is undefined due to variable/function is not declared

#include <iostream>
using namespace std;

void func(int a) {
	cout << a;
}

int main()
{
	int Value1;
	Value1 = 10;

	func(Value); 
	// error C2065: 'Value': undeclared identifier
    // Solution: func(Value1); 

	return 0;
}

Here we have not declared Value variable. So it is giving undeclared error. If we change it to func(Value1); then error will be resolve. Always check that particular variable is declared or not.

#include <iostream>
using namespace std;

int main()
{
	int Value1;
	Value1 = 10;

	func(Value1);
	// error C3861: 'func': identifier not found

	return 0;
}

Here func(int value){…} is not available so it will give error for c++ identifier not found.

Solution-2 : c++ identifier is undefined due to variable is out of Scope {..}

#include <iostream>
using namespace std;

int main()
{
	{
	 int Value1; // Variable scope will be over after {}
	}

	Value1 = 10;
    // error C2065: 'Value1': undeclared identifier

	return 0;
}

Here variable declaration scope is over once {..} is over. So outside scope if we try to access variable then it will give error for c++ identifier is undefined.

2) c++ identifier cout is undefined

#include <iostream>
int main()
{
	int Value1;
	Value1 = 10;

	cout << Value1;
	// error C2065: 'cout': undeclared identifier

	return 0;
}

Here error is coming because cout is inside std namespace.

std::cout << Value1;

If you don’t wand to add std::cout every time then you can add using namespace std; in header section so it will apply to whole file.

#include <iostream>
using namespace std; // Need to add it

Using these both solutions you can easily remove c++ identifier cout is undefined error from your program.

3) c++ identifier string is undefined

#include <iostream>
int main()
{
	string str;
	// C2065: 'string': undeclared identifier
	return 0;
}

string variable is also inside std namespace, so you will need to use std::string every time or you can add using namespace std; inside starting of file includes.

std::string str;
OR
using namespace std; 

Using this code change you can resolve c++ identifier string is undefined from your program.

4) identifier system is undefined c++

#include <stdio.h>
int main()
{
	system("pause");
	// error C3861: 'system': identifier not found
	// system is available inside #include <stdlib.h>
	return 0;
}

system() is define inside #include <stdlib.h> header file. If you have not included this file then you will get errors for identifier system is undefined c++.

Conclusion: c++ identifier is undefined

Whenever you are getting identifier is undefined error in c++ then you need to check 1) Variable name is declared or not 2) Variable or function is not out of scope 3) Proper #include file is added or not. Mostly due to these three reason error occurs. By checking coding you will able to identify issue.

See more:

C++ is widely used programming language, you can read more use of c++ in real world.