I actually intend to make a program using c++ which does the three following tasks:
1)lets me input the location and name of a jpg image file...
2)picks up the name of the file and stores it in a string...for eg if file name is myfile.jpg it picks up "myfile" and stores it in a string
3)IMP TASK: The program then puts the string obtained ie."myfile" into the description of the file......the description is the metadata of file which can be accessed by right clicking on any image and then clicking on properties.....In the detail tab there are various data like description,author,subject etc.........(i want to fill these details using c++ program....)


I just want to know how to start with the program...which libraries and functions i wud require......(and if the program cud be done easily in some another language....)

You can examine Samuel R. Buss' s glut Four Texture sample. In this sample, there is a RGBImage.h and a RGBImage.cpp to readbmp file. If you examine that, i think you'll learn how to edit jpg file after learning jpg specifications.
I can't find the link sorry and pasting the source here.

/*
 *
 * RayTrace Software Package, release 1.0.4,  February 2004.
 *
 * Author: Samuel R. Buss
 *
 * Software accompanying the book
 *		3D Computer Graphics: A Mathematical Introduction with OpenGL,
 *		by S. Buss, Cambridge University Press, 2003.
 *
 * Software is "as-is" and carries no warranty.  It may be used without
 *   restriction, but if you modify it, please change the filenames to
 *   prevent confusion between different versions.  Please acknowledge
 *   all use of the software in any publications or products based on it.
 *
 * Bug reports: Sam Buss, sbuss@ucsd.edu.
 * Web page: http://math.ucsd.edu/~sbuss/MathCG
 *
 */

#ifndef RGBIMAGE_H
#define RGBIMAGE_H

#include <stdio.h>
#include <assert.h>

// Include the next line to turn off the routines that use OpenGL
// #define RGBIMAGE_DONT_USE_OPENGL

class RgbImage
{
public:
	RgbImage();
	RgbImage( const char* filename );
	RgbImage( int numRows, int numCols );	// Initialize a blank bitmap of this size.
	~RgbImage();

	bool LoadBmpFile( const char *filename );		// Loads the bitmap from the specified file
	bool WriteBmpFile( const char* filename );		// Write the bitmap to the specified file
#ifndef RGBIMAGE_DONT_USE_OPENGL
	bool LoadFromOpenglBuffer();					// Load the bitmap from the current OpenGL buffer
#endif

	long GetNumRows() const { return NumRows; }
	long GetNumCols() const { return NumCols; }
	// Rows are word aligned
	long GetNumBytesPerRow() const { return ((3*NumCols+3)>>2)<<2; }	
	const void* ImageData() const { return (void*)ImagePtr; }

	const unsigned char* GetRgbPixel( long row, long col ) const;
	unsigned char* GetRgbPixel( long row, long col );
	void GetRgbPixel( long row, long col, float* red, float* green, float* blue ) const;
	void GetRgbPixel( long row, long col, double* red, double* green, double* blue ) const;

	void SetRgbPixelf( long row, long col, double red, double green, double blue );
	void SetRgbPixelc( long row, long col, 
					   unsigned char red, unsigned char green, unsigned char blue );

	// Error reporting. (errors also print message to stderr)
	int GetErrorCode() const { return ErrorCode; }
	enum {
		NoError = 0,
		OpenError = 1,			// Unable to open file for reading
		FileFormatError = 2,	// Not recognized as a 24 bit BMP file
		MemoryError = 3,		// Unable to allocate memory for image data
		ReadError = 4,			// End of file reached prematurely
		WriteError = 5			// Unable to write out data (or no date to write out)
	};
	bool ImageLoaded() const { return (ImagePtr!=0); }  // Is an image loaded?

	void Reset();			// Frees image data memory

private:
	unsigned char* ImagePtr;	// array of pixel values (integers range 0 to 255)
	long NumRows;				// number of rows in image
	long NumCols;				// number of columns in image
	int ErrorCode;				// error code

	static short readShort( FILE* infile );
	static long readLong( FILE* infile );
	static void skipChars( FILE* infile, int numChars );
	static void RgbImage::writeLong( long data, FILE* outfile );
	static void RgbImage::writeShort( short data, FILE* outfile );
	
	static unsigned char doubleToUnsignedChar( double x );

};

inline RgbImage::RgbImage()
{ 
	NumRows = 0;
	NumCols = 0;
	ImagePtr = 0;
	ErrorCode = 0;
}

inline RgbImage::RgbImage( const char* filename )
{
	NumRows = 0;
	NumCols = 0;
	ImagePtr = 0;
	ErrorCode = 0;
	LoadBmpFile( filename );
}

inline RgbImage::~RgbImage()
{ 
	delete[] ImagePtr;
}

// Returned value points to three "unsigned char" values for R,G,B
inline const unsigned char* RgbImage::GetRgbPixel( long row, long col ) const
{
	assert ( row<NumRows && col<NumCols );
	const unsigned char* ret = ImagePtr;
	long i = row*GetNumBytesPerRow() + 3*col;
	ret += i;
	return ret;
}

inline unsigned char* RgbImage::GetRgbPixel( long row, long col ) 
{
	assert ( row<NumRows && col<NumCols );
	unsigned char* ret = ImagePtr;
	long i = row*GetNumBytesPerRow() + 3*col;
	ret += i;
	return ret;
}

inline void RgbImage::GetRgbPixel( long row, long col, float* red, float* green, float* blue ) const
{
	assert ( row<NumRows && col<NumCols );
	const unsigned char* thePixel = GetRgbPixel( row, col );
	const float f = 1.0f/255.0f;
	*red = f*(float)(*(thePixel++));
	*green = f*(float)(*(thePixel++));
	*blue = f*(float)(*thePixel);
}

inline void RgbImage::GetRgbPixel( long row, long col, double* red, double* green, double* blue ) const
{
	assert ( row<NumRows && col<NumCols );
	const unsigned char* thePixel = GetRgbPixel( row, col );
	const double f = 1.0/255.0;
	*red = f*(double)(*(thePixel++));
	*green = f*(double)(*(thePixel++));
	*blue = f*(double)(*thePixel);
}

inline void RgbImage::Reset()
{
	NumRows = 0;
	NumCols = 0;
	delete[] ImagePtr;
	ImagePtr = 0;
	ErrorCode = 0;
}


#endif // RGBIMAGE_H
/*
 *
 * RayTrace Software Package, release 1.0.4,  February 2004.
 *
 * Author: Samuel R. Buss
 *
 * Software accompanying the book
 *		3D Computer Graphics: A Mathematical Introduction with OpenGL,
 *		by S. Buss, Cambridge University Press, 2003.
 *
 * Software is "as-is" and carries no warranty.  It may be used without
 *   restriction, but if you modify it, please change the filenames to
 *   prevent confusion between different versions.  Please acknowledge
 *   all use of the software in any publications or products based on it.
 *
 * Bug reports: Sam Buss, sbuss@ucsd.edu.
 * Web page: http://math.ucsd.edu/~sbuss/MathCG
 *
 */

#include "RgbImage.h"

#ifndef RGBIMAGE_DONT_USE_OPENGL
#include <windows.h>
#include "GL/gl.h"
#endif

RgbImage::RgbImage( int numRows, int numCols )
{
	NumRows = numRows;
	NumCols = numCols;
	ImagePtr = new unsigned char[NumRows*GetNumBytesPerRow()];
	if ( !ImagePtr ) {
		fprintf(stderr, "Unable to allocate memory for %ld x %ld bitmap.\n", 
				NumRows, NumCols);
		Reset();
		ErrorCode = MemoryError;
	}
	// Zero out the image
	unsigned char* c = ImagePtr;
	int rowLen = GetNumBytesPerRow();
	for ( int i=0; i<NumRows; i++ ) {
		for ( int j=0; j<rowLen; j++ ) {
			*(c++) = 0;
		}
	}
}

/* ********************************************************************
 *  LoadBmpFile
 *  Read into memory an RGB image from an uncompressed BMP file.
 *  Return true for success, false for failure.  Error code is available
 *     with a separate call.
 *  Author: Sam Buss December 2001.
 **********************************************************************/

bool RgbImage::LoadBmpFile( const char* filename ) 
{  
	Reset();
	FILE* infile = fopen( filename, "rb" );		// Open for reading binary data
	if ( !infile ) {
		fprintf(stderr, "Unable to open file: %s\n", filename);
		ErrorCode = OpenError;
		return false;
	}

	bool fileFormatOK = false;
	int bChar = fgetc( infile );
	int mChar = fgetc( infile );
	if ( bChar=='B' && mChar=='M' ) {			// If starts with "BM" for "BitMap"
		skipChars( infile, 4+2+2+4+4 );			// Skip 4 fields we don't care about
		NumCols = readLong( infile );
		NumRows = readLong( infile );
		skipChars( infile, 2 );					// Skip one field
		int bitsPerPixel = readShort( infile );
		skipChars( infile, 4+4+4+4+4+4 );		// Skip 6 more fields

		if ( NumCols>0 && NumCols<=100000 && NumRows>0 && NumRows<=100000  
			&& bitsPerPixel==24 && !feof(infile) ) {
			fileFormatOK = true;
		}
	}
	if ( !fileFormatOK ) {
		Reset();
		ErrorCode = FileFormatError;
		fprintf(stderr, "Not a valid 24-bit bitmap file: %s.\n", filename);
		fclose ( infile );
		return false;
	}

	// Allocate memory
	ImagePtr = new unsigned char[NumRows*GetNumBytesPerRow()];
	if ( !ImagePtr ) {
		fprintf(stderr, "Unable to allocate memory for %ld x %ld bitmap: %s.\n", 
				NumRows, NumCols, filename);
		Reset();
		ErrorCode = MemoryError;
		fclose ( infile );
		return false;
	}

	unsigned char* cPtr = ImagePtr;
	for ( int i=0; i<NumRows; i++ ) {
		int j;
		for ( j=0; j<NumCols; j++ ) {
			*(cPtr+2) = fgetc( infile );	// Blue color value
			*(cPtr+1) = fgetc( infile );	// Green color value
			*cPtr = fgetc( infile );		// Red color value
			cPtr += 3;
		}
		int k=3*NumCols;					// Num bytes already read
		for ( ; k<GetNumBytesPerRow(); k++ ) {
			fgetc( infile );				// Read and ignore padding;
			*(cPtr++) = 0;
		}
	}
	if ( feof( infile ) ) {
		fprintf( stderr, "Premature end of file: %s.\n", filename );
		Reset();
		ErrorCode = ReadError;
		fclose ( infile );
		return false;
	}
	fclose( infile );	// Close the file
	return true;
}

short RgbImage::readShort( FILE* infile )
{
	// read a 16 bit integer
	unsigned char lowByte, hiByte;
	lowByte = fgetc(infile);			// Read the low order byte (little endian form)
	hiByte = fgetc(infile);			// Read the high order byte

	// Pack together
	short ret = hiByte;
	ret <<= 8;
	ret |= lowByte;
	return ret;
}

long RgbImage::readLong( FILE* infile )
{  
	// Read in 32 bit integer
	unsigned char byte0, byte1, byte2, byte3;
	byte0 = fgetc(infile);			// Read bytes, low order to high order
	byte1 = fgetc(infile);
	byte2 = fgetc(infile);
	byte3 = fgetc(infile);

	// Pack together
	long ret = byte3;
	ret <<= 8;
	ret |= byte2;
	ret <<= 8;
	ret |= byte1;
	ret <<= 8;
	ret |= byte0;
	return ret;
}

void RgbImage::skipChars( FILE* infile, int numChars )
{
	for ( int i=0; i<numChars; i++ ) {
		fgetc( infile );
	}
}

/* ********************************************************************
 *  WriteBmpFile
 *  Write an RGB image to an uncompressed BMP file.
 *  Return true for success, false for failure.  Error code is available
 *     with a separate call.
 *  Author: Sam Buss, January 2003.
 **********************************************************************/

bool RgbImage::WriteBmpFile( const char* filename )
{
	FILE* outfile = fopen( filename, "wb" );		// Open for reading binary data
	if ( !outfile ) {
		fprintf(stderr, "Unable to open file: %s\n", filename);
		ErrorCode = OpenError;
		return false;
	}

	fputc('B',outfile);
	fputc('M',outfile);
	int rowLen = GetNumBytesPerRow();
	writeLong( 40+14+NumRows*rowLen, outfile );	// Length of file
	writeShort( 0, outfile );					// Reserved for future use
	writeShort( 0, outfile );
	writeLong( 40+14, outfile );				// Offset to pixel data
	writeLong( 40, outfile );					// header length
	writeLong( NumCols, outfile );				// width in pixels
	writeLong( NumRows, outfile );				// height in pixels (pos for bottom up)
	writeShort( 1, outfile );		// number of planes
	writeShort( 24, outfile );		// bits per pixel
	writeLong( 0, outfile );		// no compression
	writeLong( 0, outfile );		// not used if no compression
	writeLong( 0, outfile );		// Pixels per meter
	writeLong( 0, outfile );		// Pixels per meter
	writeLong( 0, outfile );		// unused for 24 bits/pixel
	writeLong( 0, outfile );		// unused for 24 bits/pixel

	// Now write out the pixel data:
	unsigned char* cPtr = ImagePtr;
	for ( int i=0; i<NumRows; i++ ) {
		// Write out i-th row's data
		int j;
		for ( j=0; j<NumCols; j++ ) {
			fputc( *(cPtr+2), outfile);		// Blue color value
			fputc( *(cPtr+1), outfile);		// Blue color value
			fputc( *(cPtr+0), outfile);		// Blue color value
			cPtr+=3;
		}
		// Pad row to word boundary
		int k=3*NumCols;					// Num bytes already read
		for ( ; k<GetNumBytesPerRow(); k++ ) {
			fputc( 0, outfile );				// Read and ignore padding;
			cPtr++;
		}
	}

	fclose( outfile );	// Close the file
	return true;
}

void RgbImage::writeLong( long data, FILE* outfile )
{  
	// Read in 32 bit integer
	unsigned char byte0, byte1, byte2, byte3;
	byte0 = (unsigned char)(data&0x000000ff);		// Write bytes, low order to high order
	byte1 = (unsigned char)((data>>8)&0x000000ff);
	byte2 = (unsigned char)((data>>16)&0x000000ff);
	byte3 = (unsigned char)((data>>24)&0x000000ff);

	fputc( byte0, outfile );
	fputc( byte1, outfile );
	fputc( byte2, outfile );
	fputc( byte3, outfile );
}

void RgbImage::writeShort( short data, FILE* outfile )
{  
	// Read in 32 bit integer
	unsigned char byte0, byte1;
	byte0 = data&0x000000ff;		// Write bytes, low order to high order
	byte1 = (data>>8)&0x000000ff;

	fputc( byte0, outfile );
	fputc( byte1, outfile );
}


/*********************************************************************
 * SetRgbPixel routines allow changing the contents of the RgbImage. *
 *********************************************************************/

void RgbImage::SetRgbPixelf( long row, long col, double red, double green, double blue )
{
	SetRgbPixelc( row, col, doubleToUnsignedChar(red), 
							doubleToUnsignedChar(green),
							doubleToUnsignedChar(blue) );
}

void RgbImage::SetRgbPixelc( long row, long col,
				   unsigned char red, unsigned char green, unsigned char blue )
{
	assert ( row<NumRows && col<NumCols );
	unsigned char* thePixel = GetRgbPixel( row, col );
	*(thePixel++) = red;
	*(thePixel++) = green;
	*(thePixel) = blue;
}


unsigned char RgbImage::doubleToUnsignedChar( double x )
{
	if ( x>=1.0 ) {
		return (unsigned char)255;
	}
	else if ( x<=0.0 ) {
		return (unsigned char)0;
	}
	else {
		return (unsigned char)(x*255.0);		// Rounds down
	}
}
// Bitmap file format  (24 bit/pixel form)		BITMAPFILEHEADER
// Header (14 bytes)
//	 2 bytes: "BM"
//   4 bytes: long int, file size
//   4 bytes: reserved (actually 2 bytes twice)
//   4 bytes: long int, offset to raster data
// Info header (40 bytes)						BITMAPINFOHEADER
//   4 bytes: long int, size of info header (=40)
//	 4 bytes: long int, bitmap width in pixels
//   4 bytes: long int, bitmap height in pixels
//   2 bytes: short int, number of planes (=1)
//   2 bytes: short int, bits per pixel
//   4 bytes: long int, type of compression (not applicable to 24 bits/pixel)
//   4 bytes: long int, image size (not used unless compression is used)
//   4 bytes: long int, x pixels per meter
//   4 bytes: long int, y pixels per meter
//   4 bytes: colors used (not applicable to 24 bit color)
//   4 bytes: colors important (not applicable to 24 bit color)
// "long int" really means "unsigned long int"
// Pixel data: 3 bytes per pixel: RGB values (in reverse order).
//	Rows padded to multiples of four.


#ifndef RGBIMAGE_DONT_USE_OPENGL

bool RgbImage::LoadFromOpenglBuffer()					// Load the bitmap from the current OpenGL buffer
{
	int viewportData[4];
	glGetIntegerv( GL_VIEWPORT, viewportData );
	int& vWidth = viewportData[2];
	int& vHeight = viewportData[3];
	
	if ( ImagePtr==0 ) { // If no memory allocated
		NumRows = vHeight;
		NumCols = vWidth;
		ImagePtr = new unsigned char[NumRows*GetNumBytesPerRow()];
		if ( !ImagePtr ) {
			fprintf(stderr, "Unable to allocate memory for %ld x %ld buffer.\n", 
					NumRows, NumCols);
			Reset();
			ErrorCode = MemoryError;
			return false;
		}
	}
	assert ( vWidth>=NumCols && vHeight>=NumRows );
	int oldGlRowLen;
	if ( vWidth>=NumCols ) {
		glGetIntegerv( GL_UNPACK_ROW_LENGTH, &oldGlRowLen );
		glPixelStorei( GL_UNPACK_ROW_LENGTH, NumCols );
	}
	glPixelStorei(GL_UNPACK_ALIGNMENT, 4);

	// Get the frame buffer data.
	glReadPixels( 0, 0, NumCols, NumRows, GL_RGB, GL_UNSIGNED_BYTE, ImagePtr);

	// Restore the row length in glPixelStorei  (really ought to restore alignment too).
	if ( vWidth>=NumCols ) {
		glPixelStorei( GL_UNPACK_ROW_LENGTH, oldGlRowLen );
	}	
	return true;
}

#endif   // RGBIMAGE_DONT_USE_OPENGL

thnxx cahitburak...but dude i suppose this is more of a window proggraming task then a jpg one...so i dont think it would require much learning of jpg since the metadata i am talking of is shown by windows(or the os)....i was supposing some windows.h functions or some other header file which wud help me in goin thru windows jpg file metadata editing......

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