fread problems or memory problems

Hi everybody.

I`m having an odd problem with my code and i`m out of ideas.

i`m using ubuntu 7.10 and eclipse with gcc.

i`m trying to read a .bmp file, here is the code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include "FifoList.h"
#include "FileLayer.h"
#include "CodeLayer.h"
#include "CapaAscii.h"
#include "BMPFileAdministrator.h"


int main (int argc, char** argv){
	FifoList* fifoListForLongitudes = createFifoList();
	FifoList* fifoListForValues = createFifoList();
	int fileLayerError = 0;
	int codeLayerError = 0;
	
	int* dataBuffer;
	int _i = 0 ;
	
	int _data;
	
	
	FILE* _bmpFile = fopen("hola.bmp", "r+b");
	BMPData* bmpData = (BMPData*)malloc(sizeof(BMPData));
	if (_bmpFile != NULL){
	
	
		printf ("algo hago\n");
	
		// aca abro el bmp
		
                errorDeArchivo = openBMPFile (_bmpFile, bmpData);
		
                if (!(feof(_bmpFile))){
			fseek (_bmpFile, 18, SEEK_SET);
			fread (dataBuffer, 4, 1, _bmpFile);
			printf("%d\n", *dataBuffer);
			_data = *dataBuffer;
			printf("%d\n", _data >> 10);
		}
		
		
		
		while(_i < 5){ 
			takeLongitudesFromFile(_bmpFile);
			
			_i++;
		}
		
		destroyFifoList (fifoListForLongitudes);
		destroyFifoList (fifoListForValues);
		free (bmpData);
		fclose (_bmpFile);
	}
	if (fileLayerError && codeLayerError && errorDeCapaAscii && errorDeArchivo){
		return 1;
	}else{
		//aca mostra el mensaje
		system("pause");
        return 0;	
	}
}

this is the code for BMPFileAdministrator.h:

Code:

typedef struct BMPDataType{
	
	int positionIndex;
	int height;
	int width;
	int startingAtByte;	
	int headerSize;
	int padding;
	int rowTwentyStartsAtByte;
} BMPData;


int openBMPFile(FILE* bmpFile, BMPData* bmpData);

[/CODE]

and here is the implementation fon openBMPFile:

Code:

int openBMPFile(FILE* bmpFile, BMPData* bmpData){
	int error = 0;
	char buffer[2];
	int* dataBuffer;
	int fileSize = 0;
	//int i = 0;
	//int j;
	//int _data;
	//int h;
		
	
	
	
		
	if (!(feof(bmpFile))){
		fread(buffer, 2, 1, bmpFile);
			
			
		if(buffer[0] == 'B' && buffer [1] == 'M'){
				
				
			fread(dataBuffer, 4, 1, bmpFile);
			fileSize = *dataBuffer;
			//printf ("%d", fileSize);
			
			fseek (bmpFile, 10, SEEK_SET);
			fread(dataBuffer, 4, 1, bmpFile);
			bmpData->startingAtByte = *dataBuffer;
			 printf("%d \n", *dataBuffer);
			
			fseek (bmpFile, 14, SEEK_SET);
			fread (dataBuffer, 4, 1, bmpFile);
			bmpData->headerSize = *dataBuffer;
			printf("%d \n", *dataBuffer);
							
			fseek (bmpFile, 18, SEEK_SET);
			fread (dataBuffer, 4, 1, bmpFile);
			bmpData->width = *dataBuffer;
			printf("%d \n", *dataBuffer);
			
			fseek (bmpFile, 22, SEEK_SET);
			fread (dataBuffer, 4, 1, bmpFile);
			bmpData->height = *dataBuffer;
			printf("%d \n", *dataBuffer);
			

			//padding expresado en bits
			bmpData->padding = 8*((fileSize - bmpData->startingAtByte)/bmpData->height) - bmpData->width;
			printf("%d \n", bmpData->padding);
			
			bmpData->rowTwentyStartsAtByte = (((bmpData->height - 20)*(bmpData->width + bmpData->padding))/8) + bmpData->headerSize;  					
			
			
		}else{
			error = 1;
		} 					
							
	}else{
		error = 1;
	}	

	return error;	
}

im getting correct values from the code that reads the header of the file, it gets the data correctly. but the problem is that after that if i want to read any further i start getting segmentation fault for stupid things like trying to do a for loop to show on the console a piece of the file using something like this

Code:

for (i = 0; i < bmpData->width; i = i +32){ 
				
					
				fread (dataBuffer, 4, 1, bmpFile);
				for (j = 31; j > -1; j--){
					_data = *dataBuffer;
					printf("%d", _data >> j);	
				}	
}

even if i comment all the code inside the for it shows segmentation fault, i comment the whole for and no segmentation fault.

i tried reading the file after it exits this method and i can read it but when i try to read the file in a while or a for loop i get the same problem, a segmentation fault. the most weird thing is that with this code in the main after the call to openBMPFIle

Code:

if (!(feof(_bmpFile))){
			fseek (_bmpFile, 18, SEEK_SET);
			fread (dataBuffer, 4, 1, _bmpFile);
			printf("%d\n", *dataBuffer);
			_data = *dataBuffer;
			printf("%d\n", _data >> 10);
		}

it reads fine but when i add afer this this code:

Code:

int i = 0;
int b = 0;
int* a;

fseek(_bmpFile, b, SEEK_SET);
fread(a, 4, 1, _bmpFile);
for (j = 31; j > -1; j--){
		_data = *a;
		//_data = _data << i;
                _data = _data >> j;
		printf("%d\n", _data );	
                i++;
}

this does not work, segmentation fault it says, but if i remove the code that uses the int i variable it works fine. meaning that the int i is the problem(?).

So this is the problem: i open a file, i read it just fine in a function up to some point and then when i trie to read it it starts trowing segmentations fault for weird things.

Thank you for your time, any opinions or help will be apreciated.

fread(a, 4, 1, _bmpFile);

your a is not initialized pointer - you have no right to write there anything

also - do not use feof to control loop - read FAQ