How to fix cpp linker undefined reference error

October 15, 2020 by Christian Longman


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Reply. Unresolved xrefs occur when a function or global variable symbol is referenced in a program, but none of the object files or libraries specified in the linking step contain a definition for that symbol.



cpp linker error undefined reference

These specific errors occur at the last stage of compilation. The stage is also called the linking stage. As the name suggests, all the code (implementation files) has been converted to object files or libraries. Now the compiler wants to tie them all together.

As a small example, the developer defined SYM in the TEST1 class, and you declared it in the TEST2 class. The linking phase is responsible for ensuring that the call to that symbol finds a valid symbol and is associated with it. If this symbol does not find TEST1 (for various reasons discussed in detail), we get this error.

Forgot To Add The Appropriate Libraries / Object Files:

This is one of the most common mistakes when a user uses library headers but forgets to add linked library files / objects or has the wrong path. If you are using developer tools like Xcode, forget to add the library search path. There was no such symbol during the binding, hence the error.

What does it mean when the linker reports that it Cannot resolve a reference?

If the linker cannot resolve normal, non-weak symbol references from previously loaded content, it tries to do so by finding the symbol in the library: if it does not find such a link, the linker indicates an error.

In Xcode, go to "Build Configuration" => "Go to Library Search Path" => Specify Library Pathteke. Similarly, follow the title search path => specify the title path

In Terminal / Makefile, you must specify all object files and libraries with -l when creating the final executable / library. So the syntax would be:

Make sure the developer has the correct symbol. If so, check if the developer has a valid path. The example above assumes all .o and libraries are in the same folder.

Mixing C With C ++, Symbols Defined In C Are Called From C ++:

Mangled C ++ function and variable names (Why: Wiki). Declaring C functions in C ++ is going to be a little tricky. And since the function / variable name has changed in the C ++ file, the function / variable definition is never found, which causes a link error. Here's an example to get it right:

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Let's say we have a void C_Method () method and we want to use it in a C ++ file. The C ++ declaration should look like this:

Adding the outer "C" tells the compiler that this method belongs to C, and does not break it. But wait, what if you want to use Do you want to read the entire header file? In this case, you need to create an external header file like this:

Alternatively, if your C library is yours, do the following right in the header:

Declared But Not Defined:

C ++ Model Issues:

An undefined / non-specialized template definition must be visible to all files that use it. In other words, don't separate implementation and reporting. And if really necessary, make sure the implementation file is added to the same group. And it fits easily. Example:

Dependent Linked Libraries

It is very important to maintain the order of library mappings when they are interdependent. The link must be in the order in which there are no dependencies on the upstream dependency.

Import Bad Modules When Working With A Codebase With Multiple Platforms / Architects:

In cross-platform code, we usually share platform-specific libraries using #defines, and misplaced #defines can lead to many errors.

To But it is the same if you use bold file libraries. Make sure they have all of the architecture you plan to use them for.

Source File Of The Same Name:

How do I fix the linker error C++ undefined symbol?

The -z defs linker option can be used to force a fatal error if there are still undefined characters. This option is recommended when creating shared objects. Shared objects that refer to symbols in an application can use the -z defs option and define symbols using an external Mapfile directive.

If the source files are organized in different folders, a file with the same name may be stored in different folders and Microsoft Visual Studio (some versions) will not be able to handle this. Since all .o files are stored in a flat directory, the new .o file replaces the old one. But this is an old problem and it may have already been solved. I am not using windows. So I can't say much about it.



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