As a beginner, if you have just written your first few C++ programs, then there is a high chance that you will come across a strange error. This error is known as the “Undefined Reference To Main C++ Error”.
While writing any C++ code, if you have made any mistake in the main() function, then you will receive such an error message. However, you should not be worried, as this error is not as intimidating as it looks.
If you want to handle errors efficiently while working with strings, understanding Exception Handling in C++ is crucial.
In this article, we will first clarify the meaning of the ‘Undefined Reference to Main’ Error and list the common causes. Later, we will show you some prevention methods as well. So, let us start our discussion.
TL;DR: ‘Undefined Reference To Main’ C++ Error
Aspect | Summary |
Meaning of the Error | The CPP compiler cannot find the proper main() function, which is required as the program’s entry point. |
Common Causes | Absent main() function where the code has functions but no main(), Incorrect return type of the main(), Case sensitivity of the main(). |
Prevention Methods |
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Real Example | A real C++ Problem Statement has been taken with the following:
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What Is The ‘Undefined Reference To Main' Error In C++?
Every C++ program has a main() function. This function acts as the main entry gate for the rest of the program. When we are compiling any C++ code, the compiler first looks for the main() function in the program.
If the main() function is not present in the code, or it is not correctly defined, then the compiler can’t find the main() function, and the compilation never happens. This causes the ‘Undefined Reference to main’ Error.
#include <iostream>
using namespace std;
int zap() // Only The Zap() Function
{
cout<<"CodingZap";
return 0;
}
In the above code, no main() function is present. There is only the zap() function. Now, if we try to execute the code, we will get the following output, which shows the ‘Undefined Reference to main’ in C++.
Why Does The ‘Undefined Reference To Main’ Error Happen In A C++ Code?
The meaning of the ‘Undefined Reference to main’ error should have become clear to you now. So, we can move ahead to some potential reasons for which such errors can happen in your C++ programs.
Let us check the following list of causes. In most cases, this error happens due to any one of them.
1. Absence Of The main() Function:
In most cases, the ‘Undefined Reference to main’ issue happens due to the absence of the main() function. A beginner programmer writes the complete code, but forgot to link it with the main() function.
#include <iostream>
using namespace std;
void add() // Only The add() Function
{
int a = 10;
int b = 20;
cout << a + b; // Adding Two Values
}
// add() Should Be Called From main()
The meaning of the ‘Undefined Reference to main’ error should have become clear to you now. So, we can move ahead to some potential reasons for which such errors can happen in your C++ programs.
Let us check the following list of causes. In most cases, this error happens due to any one of them.
1. Absence Of The main() Function:
In most cases, the ‘Undefined Reference to main’ issue happens due to the absence of the main() function. A beginner programmer writes the complete code, but forgot to link it with the main() function.
#include <iostream>
using namespace std;
void add() // Only The add() Function
{
int a = 10;
int b = 20;
cout << a + b; // Adding Two Values
}
// add() Should Be Called From main()
Here, the add() function has been defined, which adds two values. The add() function is correct, but this function should be called from the main() function, which is absent. So, the error will happen in this code.
2. Incorrect Return Type Of The main():
When a new programmer writes the main() function, they get confused about the return type. Sometimes, they remove the Return Statement from the code and make the return type ‘void’, which is not acceptable.
#include <iostream>
using namespace std;
void main() // main() Function With Void Return
{
int a = 10;
int b = 20;
cout << a * b; // Multiplying Two Values
// No Return 0 Statement
}
In the above code, the function is performing multiplication. The programmer pretended that the function was not returning anything to anyone, so he used a ‘void’ return type and removed the Return Statement, which is wrong.
3. Case Sensitivity Issues:
An individual who has newly started programming often gets confused with the Typo of the main() function. Any kind of mistake with the main() function signature can cause the ‘Undefined Reference to main’ error.
#include <iostream>
using namespace std;
int Main() // main() Function Typo Error
{
int a;
// Performing An Operation
cout << "Please Enter A Value";
cin >> a;
return 0;
}
Here, the programmer has written the code well and mentioned the correct return type as well. But, instead of writing the main() function in Lowercase, it has been written in Uppercase. So, the error will occur.
How To Prevent C++ Error ‘Undefined Reference To Main’?
After clearing the causes of ‘Undefined Reference to main’ CPP error, we will discuss some effective methods that will help prevent such errors from happening. Also, they can be used as fixing methods.
Let us check the following list, where the effective methods are discussed in a detailed manner.
1. Always Start With The main():
Whenever you are working with any C++ program, first start with the main() function. You have to always keep in mind that, without the main() function, the C++ code will not work. So, write important things only in the main().
#include <iostream>
using namespace std;
int main() // Only The add() Function
{
int a = 22;
int b = 25;
cout << "The Value Of Addition: " << a + b; // Adding Two Values
return 0;
}
Explanation Of The Program:
- Here, we are performing a simple addition. We have taken two values and added them to get the output.
- Every operation is done inside the main() function. As it is a very simple operation, no more functions are needed.
Output:
2. Use Proper Function Signature: [H3]
If you are even starting your C++ code with the main() function first, you have to keep the function signature proper. If there is any mistake in the function signature, then again such an error will prompt up.
#include <iostream>
using namespace std;
int main(int argc, char* argv[]) // This Is Extended Version Of main()
{
cout << "This Is CodingZap";
return 0;
}
/* Use Either Version Between These Two */
int main() // This Is The Normal Version Of main()
{
cout << "This Is CodingZap";
return 0;
}
Explanation Of The Code Snippet:
- Here, we are printing a message using two different function signatures of the main() function.
- You can use any one of them. But, for both cases, we will get the same output.
Output:
Real Example: Fixing ‘Undefined Reference To Main’ Error In A C++ Program
We hope the ‘Undefined Reference to main’ error and its prevention methods have become clear to you. If you still have a doubt regarding the fixing of ‘Undefined Reference to main’, then this section can help you out.
Here, we will take a real C++ problem where the error is happening and we will fix it out live. So, let us start.
Problem Statement: Write a C++ program that will divide the value 20 by the value 4.
Wrong Code:
Here, we will first show you the wrong code where ‘Undefined Reference to main’ is happening.
#include <iostream>
using namespace std;
void divide() // The divide() Function
{
// Considering The Variables
int a = 20;
int b = 4;
cout << "The Result Is: " << a / b; // Getting The Result
}
Here, the code is giving an error for the following reasons. Let us check them out.
- The divide() function has been implemented properly, but there is no main() function mentioned.
- So, the main() function is absent in the code, for which we will get the error.
Correct Code:
Now, we will show the correct version of the code, which will not cause the ‘Undefined Reference to main’.
#include <iostream>
using namespace std;
void divide() // The divide() Function
{
// Considering The Variables
int a = 20;
int b = 4;
cout << "The Result Is: " << a / b; // Getting The Result
}
int main() // main() Function Implemented With Proper Signature
{
divide(); // Calling The divide() Function
return 0;
}
Understood this code? If you have any doubts or issues related to other C++ concepts and are struggling with your homework, then you can use CodingZap’s best C++ assignment help services.
Now, let us check out the fixing methods that are used in this code to make it perfect.
- At first, Fixing Method 1 was used to implement the main() function in the program.
- Later, Fixing Method 2 was used, in which the proper function signature of main() is utilized.
Key Takeaways:
- The ‘Undefined Reference to main’ error happens when there are any issues with the main() function.
- If the main() function is not present or accessible, then such a problem can be seen.
- Absent main() function, improper function signature, typos in main() are some common causes.
- Always start with main(), use proper function signature, and all file compilation is some cure.
FAQs (Frequently Asked Question by Students)
You have to check whether you are compiling the ‘main.cpp’ with all the other classes. If the ‘main.cpp’ file is not present during compilation, the ‘Undefined Reference to main’ will happen.
If you are still getting ‘Undefined Reference to main’ error even after correctly writing everything in the main() function, then the problem might be with the Code Formatting. You have to check the Header File section.
No, in the C++ program main() function, you can’t write the ‘void main()’ instead of ‘int main()’. This is not allowed by the CPP compiler. You have to always use ‘int main()’ and return in the main() function.
