#2) When we have external variables referenced in the source file, and we have not linked the files that define these external variables. The way to fix this error is to explicitly scope the variable using ‘::’ outside the main before using it. So when we try to assign it a value in the main function, the linker doesn’t find the symbol and may result in an “unresolved external symbol” or “undefined reference”. In the above program, structure C has a static member s that is not accessible to the outside programs. int C::s // Uncomment the following line to fix the error. here we are accessing unknown memory location This indeed results in a segmentation fault. Hence when we dereference it in the next line, we are actually trying to access its unknown memory location. In the below program, we see that the pointer is pointing to NULL which means the memory location it’s pointing to is 0 i.e. #include Ī pointer must point to a valid memory location before we dereference it. When the program is executed, we get the error shown in the output. Then we try to modify this constant string. Here are some of the reasons that cause Segmentation fault error.Ĭonsider the following program wherein we have declared a constant string. It usually occurs when we try to access a memory that does not belong to the program into consideration. The error “segmentation fault (core dumped)” is an error that indicates memory corruption. But the bottom line is that the programmer has got the things wrong and in order to prevent this error they should be corrected. If any of the dependencies are missing then the compiler gives “undefined reference”.Īpart from the causes discussed above, the “undefined reference” error can occur in many other situations. If a programmer has not specified the library path properly or completely forgotten to specify it, then we get an “undefined reference” for all the references the program uses from the library.Ī programmer has to ensure that we compile all the dependencies of the project beforehand so that when we compile the project, the compiler finds all the dependencies and compiles successfully.
When we specify wrong project types in C++ IDEs like the visual studio and try to do things that the project does not expect, then, we get “undefined reference”. The way to resolve this error is to compile both the files simultaneously ( For example, by using g++).Īpart from the causes already discussed, “undefined reference” may also occur because of the following reasons. When we compile these files separately, the first file gives “undefined reference” for the print function, while the second file gives “undefined reference” for the main function. In the first file, we make use of the “print ()” function which is defined in the second file.
When this is done, the objects are not linked properly and it results in “undefined reference”.Ĭonsider the following two C++ programs. Here, we may have more than one source files and we might compile them independently. This issue can also give rise to the “undefined reference” error. Thus to prevent such errors, we simply cross-check if the definitions and usage of all the objects are matching in our program. Now the program gives the appropriate output. In order to get rid of this error, we correct the program as follows by providing the definition of the function func1. So when we compile this program, the linker error that says “undefined reference to ‘func1()’” is issued. Here we have only specified the prototype of function and then used it in the main function. The programmer has simply forgotten to define the object.Ĭonsider the following C++ program. This is the simplest reason for causing an “undefined reference” error. There are various reasons that cause an “undefined reference” error. As clear from definition, this error occurs in the later stages of the linking process. Thus when the linker cannot find the definition of a linked object, it issues an “undefined reference” error. We will discuss the possible causes of each of these errors and along with the precautions that we can take as a programmer to prevent these errors.Īn “Undefined Reference” error occurs when we have a reference to object name (class, function, variable, etc.) in our program and the linker cannot find its definition when it tries to search for it in all the linked object files and libraries.
In this tutorial, we will discuss three types of errors that are critical from any C++ programmer’s point of view.