What is an "unresolved external symbol?"

[halfpower]

I'm trying to compile something, but I have a linking error that says "unresolved external symbol." The error in it's entirety is

Linking...
Creating library E:\My System Files\vstsdk2.4\vstgui.sf\drawtest\win\Debug\drawtest.lib and object E:\My System Files\vstsdk2.4\vstgui.sf\drawtest\win\Debug\drawtest.exp
cfileselector.obj : error LNK2019: unresolved external symbol __imp__GetSaveFileNameA@4 referenced in function "public: long __thiscall VSTGUI::CFileSelector::run(struct VstFileSelect *)" (?run@CFileSelector@VSTGUI@@QAEJPAUVstFileSelect@@@Z)
cfileselector.obj : error LNK2019: unresolved external symbol __imp__GetOpenFileNameA@4 referenced in function "public: long __thiscall VSTGUI::CFileSelector::run(struct VstFileSelect *)" (?run@CFileSelector@VSTGUI@@QAEJPAUVstFileSelect@@@Z)
E:\My System Files\vstsdk2.4\vstgui.sf\drawtest\win\Debug\drawtest.dll : fatal error LNK1120: 2 unresolved externals

What causes this? How are such errors fixed?

 

[screw3d]

It means that you are probably missing some libraries that you are supposed to include with whatever you are compiling..

 

[halfpower]

Are these libraries .lib files or .h files?

 

[Nothinman]

The .h files are the headers with the definitions of functions, variables, classes, etc and the .lib files should be what is actually linked against.

 

[Mark R]

You need to tell the linker to use/where to find the .lib files that your project needs.

The project has already compiled so the compiler was able to find the .h files.

 

[halfpower]

Say I now have the following error message:

Linking...
LINK : fatal error LNK1104: cannot open file 'zlib.lib'

Why can't the compiler open 'zlib.lib'? I don't know where 'zlib.lib' would be. I'm not positive I compiled to a file named 'zlib.lib'. I have a 'zutil.obj' but I don't think that is the same thing.

 

[Nothinman]

zlib is a seperate project, are you sure you have a copy?

 

[halfpower]

I have the source for zlib. The source files are listed in the solution explorer in Visual C++.