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The C Users' Group Library 1994 August
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wc-cdrom-cusersgrouplibrary-1994-08.iso
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v_06_04
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v6n4016a.txt
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1989-09-28
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struct
{
int total;
char date[9];
} customer_header;
struct
{
int code;
char name[41];
char address[2][41];
} customer_record;
#include <stdio.h>
/* Misc. data */
FILE *customer_file;
int open_customer()
{
/* Open as read/write */
if ((customer_file = fopen("customer.dat", "r++")) == NULL)
{
/* Does not exist, try creating it */
if ((customer_file = fopen("customer.dat", "w++")) == NULL)
{
printf("Can't open customer.dat, error %d.\n", errno);
exit(errno);
}
/* Write out a initial header record */
memset(&customer_header, 0, sizeof (customer_header));
write_customer_header();
}
else
/* Read the header record */
fread(&customer_header, sizeof (customer_header), 1, customer_file);
}
/* Write the header record */
int write_customer_header()
{
fseek(customer_file, 0L, 0);
return fwrite(&customer_header, sizeof (customer_header), 1,
customer_file);
}
/* Read record */
int read_customer(record)
int record;
{
fseek(customer_file, (long) record * sizeof (customer_record)
+ sizeof (customer_header), 0);
return fread(&customer_record, sizeof (customer_record), 1,
customer_file);
}
/* Write record */
int write_customer(record)
int record;
{
fseek(customer_file, (long) record * sizeof (customer_record)
+ sizeof (customer_header), 0);
return fwrite(&customer_record, sizeof (customer_record), 1,
customer_file);
}
/* Delete a record (slow method ) */
int delete_customer(record)
int record;
{
int i;
for (i = record; i < customer_header.total - 1; i++)
{
read_customer(i + 1);
write_customer(i);
}
customer_header.total--;
write_customer_header();
}