Question: I'm using Qt Creator running with the mingw C++ compiler to compile some C sources I obtained from an institution known as the NBIS.
I'm trying to extract just the code that will allow me to decode images encoded in the WSQ image format.

Unfortunately I'm getting messages that I have "multiple definitions" of certain functions
which is contradicted by a grep search, as well as complaints of undefined functions which are indeed defined in a single C file in each case.
I looked at the include files and these functions do have the word extern before them in the declarations.
As for the error messages of "multiple definitions" the linker says "first defined here" and only gives one object file in each case.

All C files have a C extension.

I should add that I'm getting strange messages when I look at the compiler outout like this:
Makefile.Debug:427: warning: overriding recipe for target 'debug/huff.o' 
(it is true that I have two files called huff.c,but in different directories)

Answer: 
There's no automatic function that I know, but it can be easily done manually.

1. Remove `Pods` folder near your `Podfile`
2. Remove next files: `Podfile` and `Podfile.lock`
3. Remove generated `<Project_Name>.workspace` file
4. Open your `xcodeproj` file and in `Xcode`:
	* Remove reference to `Pods-<YOUR_TARGET>.xcconfig` file at the end of root folder ![enter image description here](https://i.stack.imgur.com/YVPmF.png)
	* Open project setting and choose `Build Phases` tab in your target setting:
	Remove here two phases: `Check Pods Manifest.lock` and `Copy Pods Resources`![enter image description here](https://i.stack.imgur.com/5nBQM.png)![enter image description here](https://i.stack.imgur.com/iy7UJ.png)
	* Open 'Build Phases' - > `Link Binary With Libraries` and remove all links that starts from `libPods...` ![enter image description here](https://i.stack.imgur.com/U4y8h.png)
	* Switch to project settings and deselect (must be `None` everywhere if you haven't created before) configuration sets if there are any at `Info` tab.![enter image description here](https://i.stack.imgur.com/mCuSi.png)
### Self Answer

While the answer by @Ossir works properly, I have found one library called [cocoapods-deintegrate](https://github.com/kylef/cocoapods-deintegrate) that takes charge of all the work that deintegrate CocoaPods from your project.

In order to use it, you first install it by `gem install cocoapods-deintegrate` (*sudo* might be required) and then just `pod deintegrate` from your project root. It still leaves *Podfile*, *Podfile.lock*, and *.xcworkspace/*.