at åbne en fil og bruge den

Kode 

FILE *fopen( const char *filename, const char *mode );

FILE *_wfopen( const wchar_t *filename, const wchar_t *mode );

The character string mode specifies the type of access requested for the file, as follows:

"r"

Opens for reading. If the file does not exist or cannot be found, the fopen call fails.

"w"

Opens an empty file for writing. If the given file exists, its contents are destroyed.

"a"

Opens for writing at the end of the file (appending) without removing the EOF marker before writing new data to the file; creates the file first if it doesn’t exist.

"r+"

Opens for both reading and writing. (The file must exist.)

"w+"

Opens an empty file for both reading and writing. If the given file exists, its contents are destroyed.

"a+"

Opens for reading and appending; the appending operation includes the removal of the EOF marker before new data is written to the file and the EOF marker is restored after writing is complete; creates the file first if it doesn’t exist.

Kode 

/* FOPEN.C: This program opens files named "data"
 * and "data2".It  uses fclose to close "data" and
 * _fcloseall to close all remaining files.
 */

#include <stdio.h>

FILE *stream, *stream2;

void main( void )
{
   int numclosed;

   /* Open for read (will fail if file "data" does not exist) */
   if( (stream  = fopen( "data", "r" )) == NULL )
      printf( "The file 'data' was not opened\\n" );
   else
      printf( "The file 'data' was opened\\n" );

   /* Open for write */
   if( (stream2 = fopen( "data2", "w+" )) == NULL )
      printf( "The file 'data2' was not opened\\n" );
   else
      printf( "The file 'data2' was opened\\n" );

   /* Close stream */
   if( fclose( stream ) )
      printf( "The file 'data' was not closed\\n" );

   /* All other files are closed: */
   numclosed = _fcloseall( );
   printf( "Number of files closed by _fcloseall: %u\\n", numclosed );
}

Kode 

size_t fread( void *buffer, size_t size, size_t count, FILE *stream );

Kode 

/* FREAD.C: This program opens a file named FREAD.OUT and
 * writes 25 characters to the file. It then tries to open
 * FREAD.OUT and read in 25 characters. If the attempt succeeds,
 * the program displays the number of actual items read.
 */

#include <stdio.h>

void main( void )
{
   FILE *stream;
   char list[30];
   int  i, numread, numwritten;

   /* Open file in text mode: */
   if( (stream = fopen( "fread.out", "w+t" )) != NULL )
   {
      for ( i = 0; i < 25; i++ )
         list[i] = (char)('z' - i);
      /* Write 25 characters to stream */
      numwritten = fwrite( list, sizeof( char ), 25, stream );
      printf( "Wrote %d items\\n", numwritten );
      fclose( stream );

   }
   else
      printf( "Problem opening the file\\n" );

   if( (stream = fopen( "fread.out", "r+t" )) != NULL )
   {
      /* Attempt to read in 25 characters */
      numread = fread( list, sizeof( char ), 25, stream );
      printf( "Number of items read = %d\\n", numread );
      printf( "Contents of buffer = %.25s\\n", list );
      fclose( stream );
   }
   else
      printf( "File could not be opened\\n" );
}