Linker error undefined reference to. An included library; Dev C linker errors, undefined reference; Help me code this problem in c c or java; SIGSEGV in C; undefined reference when calling c func from c; LIBSSH2-DEV C Integration issue Linker error undefined reference to `libssh2 linking c and c objects caused compile eror. By including the header in your main file, the compiler is informed of the description of class Hash when compiling the file, but not how class Hash actually works. When the linker tries to create the entire program, it then complains that the implementation (toHash::insert(int, char)) cannot be found. Showing links to tutorials is useless, we need to see, what you did. Were you able to build the opencv libs? (in that case it's only a problem of 'how to use them' now. (and probably noone else is using dev-cpp here, so don't expect much, if it is related to that).

• Dev C++ Undefined Reference Form
• Dev C++ Undefined Reference To Wsastartup@8'
• Dev C++ Undefined Reference To Winmain
• Dev C++ Undefined Reference Page

Dev C linker errors, undefined reference; Make File Undefined Reference. Undefined reference to destuctor in C; undefined reference when calling c func from c; LIBSSH2-DEV C Integration issue Linker error undefined reference to `libssh2 linking c and c objects caused compile eror: undefined reference. When vtables are used, every polymorphic class has a vtable somewhere in the program; you can think of it as a (hidden) static data member of the class. Every object of a polymorphic class is associated with the vtable for its most-derived class. By checking this association, the.

I thought I was finished with my code until I tried to compile it and came out with an error that I really don't know where it's coming from. Can anyone look over and see if they can find the source of the error?
Please and thank you!

These are the errors I'm getting:

/cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:10: undefined reference to Dynque<char>::Dynque()' makefile:44: recipe for targetProgram5.exe' failed
/cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:18: undefined reference to Dynque<char>::enqueue(char)' /cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:25: undefined reference toDynque<char>::dequeue(char&)'
/cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:28: undefined reference to Dynque<char>::isEmpty()' /cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:31: undefined reference toDynque<char>::~Dynque()'
/cygdrive/c/Users/Shelby Jr/workspace/Program5/Debug/./file_filter.cpp:31: undefined reference to `Dynque<char>::~Dynque()'

Dynqueue.h

Dynqueue.cpp

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sepp2k378

When defining template functions or member functions of template classes, you can't put the definitions in a separate file from the declaration. Both the declaration and the definition need to be visible to the code that uses your functions. So you need to put the contents of Dynqueue.cpp into Dynqueue.h instead.

And yes, that's the complete opposite of what you're usually supposed to do, but that's how it is.

Introduction

In this article I’ll be looking at the “undefined reference” error message (or “unresolved external symbol, for Visual C++ users). This is not actually a message from the compiler, but is emitted by the linker, so the first thing to do is to understand what the linker is, and what it does.

Linker 101

To understand the linker, you have to understand how C++ programs are built. For all but the very simplest programs, the program is composed of multiple C++ source files (also known as “translation units”). These are compiled separately, using the C++ compiler, to produce object code files (files with a .o or a .obj extension) which contain machine code. Each object code file knows nothing about the others, so if you call a function from one object file that exists in another, the compiler cannot provide the address of the called function.

This is where the the linker comes in. Once all the object files have been produced, the linker looks at them and works out what the final addresses of functions in the executable will be. It then patches up the addresses the compiler could not provide. It does the same for any libraries (.a and .lib files) you may be using. And finally it writes the executable file out to disk.

The linker is normally a separate program from the compiler (for example, the GCC linker is called ld) but will normally be called for you when you use your compiler suite’s driver program (so the GCC driver g++ will call ld for you).

Traditionally, linker technology has lagged behind compilers, mostly because it’s generally more fun to build a compiler than to build a linker. And linkers do not necessarily have access to the source code for the object files they are linking. Put together, you get a situation where linker errors, and the reasons for them, can be cryptic in the extreme.

Undefined reference

Put simply, the “undefined reference” error means you have a reference (nothing to do with the C++ reference type) to a name (function, variable, constant etc.) in your program that the linker cannot find a definition for when it looks through all the object files and libraries that make up your project. There are any number of reasons why it can’t find the definition – we’ll look at the commonest ones now.

No Definition

Probably the most common reason for unresolved reference errors is that you simply have not defined the thing you are referencing. This code illustrates the problem:

Here, we have a declaration of the function foo(), which we call in main(), but no definition. So we get the error (slightly edited for clarity):

The way to fix it is to provide the definition:

Wrong Definition

Another common error is to provide a definition that does not match up with declaration (or vice versa). For example, if the code above we had provided a definition of foo() that looked like this:

then we would still get an error from the linker because the signatures (name, plus parameter list types) of the declaration and definition don’t match, so the definition actually defines a completely different function from the one in the declaration. To avoid this problem, take some care when writing declarations and definitions, and remember that things like references, pointers and const all count towards making a function signature unique.

Didn’t Link Object File

This is another common problem. Suppose you have two C++ source files:

and:

If you compile f1.cpp on its own you get this:

Dev C++ Undefined Reference Form

and if you compile f2.cpp on its own, you get this even more frightening one:

In this situation, you need to compile both the the source files on the same command line, for example, using GCC:

or if you have compiled them separately down to object files:

For further information on compiling and linking multiple files in C++, particularly with GCC, please see my series of three blog articles starting here.

Dev C++ Undefined Reference To Wsastartup@8'

Wrong Project Type

The linker error regarding WinMain above can occur in a number of situations, particularly when you are using a C++ IDE such as CodeBlocks or Visual Studio. These IDEs offer you a number of project types such as “Windows Application” and “Console Application”. If you want to write a program that has a int main() function in it, always make sure that you choose “Console Application”, otherwise the IDE may configure the linker to expect to find a WinMain()I d rather listen to an auto tuned free. function instead.

No Library

To understand this issue, remember that a header file (.h) is not a library. The linker neither knows nor cares about header files – it cares about .a and .lib files. So if you get a linker error regarding a name that is in a library you are using, it is almost certainly because you have not linked with that library. To perform the linkage, if you are using an IDE you can normally simply add the library to your project, if using the command line, once again please see my series of blog articles on the GCC command line starting here, which describes some other linker issues you may have.

Dev C++ Undefined Reference To Winmain

Dev C++ Undefined Reference Page

Conclusion

The unresolved reference error can have many causes, far from all of which have been described here. But it’s not magic – like all errors it means that you have done something wrong, in you code and/or your project’s configuration, and you need to take some time to sit down, think logically, and figure out what.