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Undefined Reference Problem

SuperStinger (84)
Hi all, this is a really wierd problem as I have not come across it before.

Some info before I start:
IDE: CodeBlocks 13.12
OS: Windows 7
Language: plain C

I have two files io.c and io.h.

Im currently working on a function called 'IO_Append_File' in io.c and I wanted to test some of the function before continuing to finish it. It uses a function which I have not written a definition for yet, 'IO_Close_File'. This means it is declared in the io.h file. For some reason, even though I am #include-ing io.h, it spits the error 'undefined reference to 'IO_Close_File'.

Here are the files:

io.c ( errors are at line 81 and 96 )
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "io.h"
#include "general.h"

void setUpFile ( FILE* fp )
{
	//Go to beginning of file
	fseek ( fp, 0, SEEK_SET );

	//Write for this systems endianness ( 4-byte integer to start of file )
	unsigned int iPut = 1;
	fwrite ( &iPut, sizeof ( int ), 1, fp );

	//Write 0 as a 4-byte integer afterwards ( for error checking )
	iPut = 0;
	fwrite ( &iPut, sizeof ( int ), 1, fp );
}

IO_File* IO_Append_File ( char* fileName, unsigned int sugAlloc )
{
	//Open for reading and writing in binary mode
	int isNew = 0;
	FILE* fp = fopen ( fileName, "rb+" );
	if ( fp == NULL )
	{
		fp = fopen ( fileName, "wb+" );
		isNew = 1;
	}

	if ( fp == NULL )
	{
		printf ( "IO File Error: File Error\n" );
		return NULL;
	}

	//Allocate Struct needed for this
    IO_File* filePtr = malloce ( sizeof ( IO_File ) );
    memset ( filePtr, 0, sizeof ( IO_File ) );

    //Transfer File Pointer
    filePtr->fp = fp;

	//Get endianness of this machine
	int lilEnd = isLittleEndian();

	//If the file is not newly created, read all data into the IO_File struct
	if ( isNew == 0 )
	{
		//Get first 4 bytes as an integer to check endianness of stored file
		//---

		//Read the integer
		unsigned long endianInt = 0;
		fread ( &endianInt, sizeof ( long ), 1, fp );

		//Check to see if fread failed ( cut short ) by reaching end of file
		if ( feof ( fp ) )
		{
			//If so, fix the file ( Set up Endianness and empty int )
			setUpFile ( fp );
		}
		else
		{
			if ( endianInt == 1 )
			{
				//Is the Endianness of this machine
				filePtr->littleEndian = lilEnd;
			}
			else if ( endianInt == 16777216 )
			{
				//Opposite of the endianness of this machine
				filePtr->littleEndian = !lilEnd;
			}
			//Anything else means an error for the file
			else
			{
				//Unload all allocations and file pointers
				printf ( "IO File Error: Endian Incorrect\n" );
				IO_Close_File ( filePtr );
				return NULL;
			}

			//Make sure the second 4 byte integer is empty ( just a simple check )
			//---

			//Load what should be an empty value
			unsigned int emptyVal = 1;
			fread ( &emptyVal, sizeof ( int ), 1, fp );

            //Make sure its an empty value
            if ( emptyVal != 0 )
			{
				printf ( "IO File Error: Empty Value not Empty\n" );
				IO_Close_File ( filePtr );
				return NULL;
			}

			//Load all variables within the files
			//---

			//Count how many variables there are
			//Note: A Null pointer will signify the end of the header
            unsigned int varPtr = 0;
            int varAmount = 0;
            do
			{
				fread ( &varPtr, sizeof ( int ), 1, fp );
				varAmount++;
			} while ( varPtr != 0 && !feof ( fp ) );
			filePtr->varAmount = varAmount;

			//LEFT OFF
            //Allocate the
		}
	}
	//If the file is new, Initialise it
	else
	{
		//Set up the file with Endian indicator and empty Int
		setUpFile ( fp );
	}

	//Initialise Variable array
	filePtr->varAmount = 0;
	filePtr->fileData = NULL;

	return filePtr;
}


io.h
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#ifndef IO_H_INCLUDED
#define IO_H_INCLUDED

#define IO_DATA_BIG_BLOCK 1
#define IO_INDEX_OUT_OF_RANGE 3

#define FILE_BLOCK_PTR_SIZE sizeof ( int )
#define START_FILE_POS 8

//These many index of IO_File_Data are allocated in advance
//Note: not implemented yet
#define BLOCK_PTR_ALLOC_PADDING 10

typedef struct
{
	//The direct Pointer to the variable in the file
	unsigned int pData;

	//The size of the data
	unsigned int dataSize;
} IO_File_Data;

typedef struct
{
	//Pointer to an array of variable indexes
	IO_File_Data* fileData;

	//Amount of Variables currently in the file ( size of fileData )
	unsigned int varAmount;

	//Pointer to the File
	FILE* fp;

	//The endianness of the file ( is it little endian? )
	int littleEndian;
} IO_File;

//Opens a file for reading and writing
//If the file does not exist, it creates the file and sets it up
//If the file does exist, it reads all the data into memory as variables
//fileName is the path to the file to be opened
//On success, returns a pointer to the struct holding possible data and information on file
//On failure, returns a null pointer
IO_File* IO_Append_File ( char* fileName, unsigned int sugAlloc );

//Frees all dynamic allocations and closes the file pointer
void IO_Close_File ( IO_File* filePtr );

//Writes data to a particular index ( block ) in the file
//Will return error code IO_DATA_BIG_BLOCK if the data size is too big for the block pointer
//If the index is in the centre, I.E. has data behind it and/or data infront of it...
//...Data infront will be pushed forward. This is an expensive operation. ...
//...dataSize should be checked if this operation is not wanted to occur.
int IO_Write_Data ( IO_File* filePtr, int index, char* data, int dataSize );

//Grabs data from a particular index in the file
//This is done by looking at the block pointer at the given index
int IO_Get_Data ( IO_File* filePtr, int index, char* buffer, int bufferSize );

#endif // IO_H_INCLUDED


Could it be just some silly error that I have not noticed yet?

Many Thanks,
Super_Stinger
ne555 (10692)
> I wanted to test some of the function before continuing to finish it
> It uses a function which I have not written a definition for yet,
¿what do you expect to happen then?
If you try to use a function for which there is no provided definition, you'll get an "you are trying to use a function but you haven't provided a definition for it" error
That's what undefined reference means.
SuperStinger (84)
Yes, Yes I know.

I thought that if you declare a function in the .h file, but not provide a definition ( so its still declared ), it will compile fine. Indeed using the function will produce unexpected results, but for testing other parts of the program, i just need it to compile. Do I have to provide a definition as well as the declaration for the compiler to be happy? ( I thought that it did not need to be ).
Last edited on
TheIdeasMan (6782)
Hi,

Just provide a minimal stub:

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void IO_Close_File ( IO_File* filePtr ) {
    printf ("In the IO_Close_File Function");
}


Or, hell, even try empty braces :+)

Btw, you should make use of the return values from functions, by assigning them to a variable. For example fread returns a size_t value.

Hope my 1 cent worth helped a little
SuperStinger (84)
Indeed it has TheIdeasMan, many thanks!

Yep, thats what I do now and it works!
ne555 (10692)
> I thought that if you declare a function in the .h file, but not provide a definition
> it will compile fine.
undefined reference is a linker error, if it reached the linker stage then it did compile fine.


> Just provide a minimal stub:
that may be error prone, the code would build fine and the lack of implementation would be manifested in logic errors.
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