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RECORDS1.C
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─────Run-Time Library───────────────────────────────────────────────────────
/* RECORDS1.C illustrates reading and writing of file records using seek
* functions including:
* fseek rewind ftell
*
* Other general functions illustrated include:
* tmpfile _rmtmp fread fwrite
*
* Also illustrated:
* struct
*
* See RECORDS2.C for a version of this program using fgetpos and fsetpos.
*/
#include <stdio.h>
#include <io.h>
#include <string.h>
/* File record */
struct RECORD
{
int integer;
long doubleword;
double realnum;
char string[15];
} filerec = { 0, 1, 10000000.0, "eel sees tar" };
void main()
{
int c, newrec;
size_t recsize = sizeof( filerec );
FILE *recstream;
long recseek;
/* Create and open temporary file. */
recstream = tmpfile();
/* Write 10 unique records to file. */
for( c = 0; c < 10; c++ )
{
++filerec.integer;
filerec.doubleword *= 3;
filerec.realnum /= (c + 1);
_strrev( filerec.string );
fwrite( &filerec, recsize, 1, recstream );
}
/* Find a specified record. */
do
{
printf( "Enter record betweeen 1 and 10 (or 0 to quit): " );
scanf( "%d", &newrec );
/* Find and display valid records. */
if( (newrec >= 1) && (newrec <= 10) )
{
recseek = (long)((newrec - 1) * recsize);
fseek( recstream, recseek, SEEK_SET );
fread( &filerec, recsize, 1, recstream );
printf( "Integer:\t%d\n", filerec.integer );
printf( "Doubleword:\t%ld\n", filerec.doubleword );
printf( "Real number:\t%.2f\n", filerec.realnum );
printf( "String:\t\t%s\n\n", filerec.string );
}
} while( newrec );
/* Starting at first record, scan each for specific value. The following
* line is equivalent to:
* fseek( recstream, 0L, SEEK_SET );
*/
rewind( recstream );
do
{
fread( &filerec, recsize, 1, recstream );
} while( filerec.doubleword < 1000L );
recseek = ftell( recstream );
/* Equivalent to: recseek = fseek( recstream, 0L, SEEK_CUR ); */
printf( "\nFirst doubleword above 1000 is %ld in record %d\n",
filerec.doubleword, recseek / recsize );
/* Close and delete temporary file. */
_rmtmp();
}
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