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C++ Errors: Unresolved External Symbol, Undefined Reference To

This post will explain C++ Errors’ undefined reference to. We will go over the crucial mistakes that we frequently encounter in C++ that are equally vital. Apart from the system and semantic error’s and exceptions that happen from time to time, we likewise get other critical errors that affect programs’ running.

These mistakes mostly take place towards the completion of the program at runtime. Sometimes the program provides the correct output, and then the error takes place.

C++ Errors: Unresolved External Symbol, Undefined Reference To

In this article, you can know about undefined reference to here are the details below;

What You Will Learn: [program] Important C++ Errors

In this tutorial, we will discuss three kinds of mistakes that are critical from any C++ developer’s perspective.

  • – Undefined reference
  • – Segmentation fault (core dumped).
  • – Unresolved external symbol.

We will go over the possible causes of each of these errors and the safety measures that we can take as a programmer to prevent these errors.

Let’s begin!!

Undefined Reference.

An “Undefined Reference” error’s occurs when we have a reference to an object name (class, function, variable, and so on) in our program, and the linker cannot find its definitions when it tries to search for it in all the related item files and libraries. You can also check another post like how to fix 0xc1900101.

Thus, when the linker cannot find a related item’s meaning, it releases an “undefined reference” error. As clear from the definition, this error happens in the later stages of the linking procedure. Numerous factors cause an “undefined reference” mistake.

We discuss some of these factors below:

# 1) No Definition Provided For Object.

This is the most essential factor for causing an “undefined reference” mistake. The programmer has just forgotten to define the item.

Consider the following C++ program. Here we have just specified the model of function and then utilized it in the main function.


int func1();.

int main().


So when we compiles this program, the linker error states “undefined reference to ‘func1()'” is released.

To get rid of this mistake, we fix the program as follows by providing the meaning of the function func1. Now the program offers the appropriate output.

#include using namespace sexually transmitted disease.

int func1();.

int main().


int func1()

cout<<” hello, world!!”;.


Hi, world!!

# 2) Wrong Definition (signatures do not match) Of Objects Used.

Yet another cause for “undefined reference” mistake is when we specify wrong meanings. We use any item in our program, and its meaning is something different.

Think about the following C++ program. Here we have phoned to func1 (). Its prototype is int func1 (). However, its meaning does not match with its model. As we see, the meaning of the function includes a specification to the function.

Therefore when the program is put together, the collection succeeds because of the prototype and function call match. But when the linker attempts to connect the function call with its definition, it finds the problems and issues the error as “undefined reference”.


using namespace std;.

int func1();.

int primary().

int func1( int n)


Thus to prevent such errors, we merely cross-check if the definitions and use of all the things match our program.

# 3) Object Files Not Linked Properly.

This issue can also trigger the “undefined reference” error. Here, we might have more than one source files, and we might assemble them independently. When this is done, the items are not connected correctly, leading to “undefined reference”.

Think about the following two C++ programs. In the first file, we use the “print ()” function, defined in the 2nd file. When we put together these files separately, the first file offers “undefined reference” for the print function, while the 2nd file gives “undefined reference” for the main function.

int print();.

int primary().


int print()

return 42;.


The method to solve this error is to assemble both the files all at once (For example, by utilizing g++).

Apart from the causes already discussed, “undefined reference” might likewise occur for the following reasons.

# 4) Wrong Project Type.

When we specify incorrect project types in C++ IDEs like the visual studio and try to do things that the task does not expect, we get “undefined reference”.

# 5) No Library.

Suppose a programmer has not defined the library course properly or completely forgotten to define it. In that case, we get an “undefined reference” for all the references the program utilizes from the library.

# 6) Dependent Files Are Not Compiled.

A developer has to make sure that we assemble all the project dependencies in advance so that when we assemble the job, the compiler discovers all the dependencies and assembles them successfully. If any of the dependencies are missing out on, then the compiler offers “undefined reference”.

Apart from the cases discussed above, the “undefined reference” error can occur in lots of other situations. However, the bottom line is that the developer has got things incorrect, and to avoid this mistake, they must be corrected.

Division Fault (core disposed).

The mistake “segmentation fault (core discarded)” is an error that shows memory corruption. It usually takes place when we try to access a memory that does not belong to the program into factor to consider.

Here are some of the reason’s that trigger the Segmentation fault mistake.

# 1) Modifying The Constant String.

Think about the following program wherein we have stated a constant string. Then we attempt to modify this consistent string. When the program is performed, we get the mistake displayed in the output.


int primary().


# 2) Dereferencing Pointer.

A guideline needs to indicate a valid memory place before dereference it. In the below programs, we see that the guideline indicates NULL, which suggests the memory location it’s indicating is 0, i.e. void.

Thus when we dereference it in the next line, we are, in fact, trying to access its unknown memory location. This undoubtedly leads to a division fault. Also, check how to fix hulu proxy error.


utilizing namespace std;.

int main().

Here we are accessing an unidentified memory place.

* ptr = 1;.

cout << * ptr;.

return 0;.


Division fault.

The next program reveals a comparable case. In this program, likewise, the tip is not indicating valid data. An uninitialized pointers is as good as NULL, and for this reason, it likewise points to an unknown memory location. Therefore when we try to dereference it, it leads to a segmentation fault.

#include using namespace sexually transmitted disease;

int primary().

Int * p;

cout<< * p;.

return 0;.


Segmentation fault.

In order to avoid such errors, we have to ensure that our tip variables in the program indicate valid memory locations always.

# 3) Stack Overflow.

When we have recursive contact our program, they eat up all the memory in the stack and cause the stack to overflow. In such cases, we get the division fault as lacking stack memory is also a kind of memory corruption.

Consider the below program where we compute the factorial of a number recursively. Keep in mind that our base condition tests if the number is 0 and then returns 1. This program works perfectly for positive numbers.

However, what happens when we actually pass a negative number to a factorial function? Well, as the base condition is not offered for the negative numbers, the function doesn’t know where to stop and thus results in a stack overflow.

This is displayed in the output below that offers division fault.


using namespace std;.

int factorial( int n).

if( n == 0).

return factorial( n-1) * n;.

int main().

cout<< factorial( -1 );.


Segmentation fault (core dumped).

Now in order to repair this mistake, we slightly alter the base condition and also specify the case for unfavourable numbers as revealed below.


utilizing namespace std;.

int factorial( int n).

What about n < 0?

if( n <= 0).

Return 1;

return factorial( n-1) * n;.

int main().

cout<<” Factorial output:”<< factorial( -1 );.


Factorial output:1.

Now we see that the division fault is looked after, and the program works fine.

Unresolved External Symbol.

The unresolved external symbols is a linker error that indicates it can not discover the symbol or its referral during the connecting process. The mistake is similar to “undefined reference” and is provided interchangeably.

We have actually provided two circumstances below where this error can happen.

# 1) When we refer to a structure variable in the program which contains a static member.


struct C

static int s;.


// int C:: s;// Uncomment the following line to repair the mistake.

int primary()


In the above programs, structure C has a fixed member s that is not accessible to the outside programs. So when we attempt to designate it worth in the main function, the linker does not find the symbol and may lead to an “unresolved external symbol” or “undefined reference”. You can also check another post about how to fix no valid ip configuration ethernet.

The way to repair this error is to explicitly scope the variable utilizing ‘::’ outside the primary prior to using it.

# 2) When we have externals variables referenced in the source file, and we have actually not linked the files that specify these external variables.

This case is demonstrated listed below:.



using namespace sexually transmitted disease;.

extern int i;.

extern void g();.

void f()



int main()


In general, in the case of an “unresolved external symbol”, the put together code for any things like function fails to find a sign to which it makes a recommendation, possibly since that sign is not specified in the object files or any of the libraries specified to the linker.


In this tutorial, we discussed some major mistakes in C++ that are critical and can impact the program circulation and might even result in an application crash. We checked out everything about Segmentation fault, Unresolved external symbol, and Undefined reference in detail.

Although these mistakes can take place anytime, from the causes that we discussed, we understand that we can quickly avoid them by thoroughly establishing our program.


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