Multiple Declarations of [variable name] - c

Question

I am working on a header file that does a couple of functions for me. I include the header file in two seperate files, the c file and the main file.
I use #ifndef and #def but it looks like it still gets compiled twice, because during the linking process I get serveral
multiple declarations of ...
errors.
PLL header file
#ifndef PLL_HEADER
#define PLL_HEADER
/********************************************************************
* includes
********************************************************************/
#include "board.h"
#include "pin_mux.h"
#include "clock_config.h"
#include "PITDriver.h"
// Some more stuff
#endif
Here is the relevant log data
[compiling stuff]
Building target: PLL Function.axf
Invoking: MCU Linker
[other linker stuff]
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:45: multiple definition of `accumulateVal'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:45: first defined here
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:46: multiple definition of `getValOne'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:46: first defined here
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:47: multiple definition of `getValTwo'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:47: first defined here
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:48: multiple definition of `countTo'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:48: first defined here
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:49: multiple definition of `runUntil'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:49: first defined here
./source/main.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:50: multiple definition of `currentValue'
./source/PLL.o:C:\Users\mailn\Desktop\Work\Sparton\MCUXPresso Workstation\PLL Function\Debug/../source/PLL.h:50: first defined here
collect2.exe: error: ld returned 1 exit status
make: *** [makefile:39: PLL Function.axf] Error 1

Answer 1

Correction made according to the comment of #Peter
In C you can only put variable definitions in a header if it is only included in one compilation unit.
You seem to have two compilation unit :
one that compiles your PLL.h and PLL.c to create PLL.o
one that compiles your main.c and PLL.h to create main.o
Both of your objects files contain the variables that you have defined in PLL.h and therefore when you hit the linker it throws an error because the variables have been declared twice (once in each object file).
To correct this error you can either change the way you compile to merge your two compilation unit. Or (if you use an IDE that handles automatically your compilation) you can apply the following changes to avoid defining the variable in your header.
In the header : (change the definition to a declaration)
extern int x;
In a source file : (define the variable)
int x;