How to Read data and write data C programming - c

Question

#include <stdio.h>
#include <stdlib.h>
struct customer {
char fname[20],lname[20];
int acct_num;
float acct_balance;
};
void main ()
{
FILE *outfile;
struct customer input;
// open Accounts file for writing
outfile = fopen ("C:\\Users\\Admin\\Desktop\\read\\per.dat","w");
if (outfile == NULL)
{
fprintf(stderr, "\nError opening accounts.dat\n\n");
exit (1);
}
// instructions to user
printf("Enter \"stop\" for First Name to end program.");
// endlessly read from keyboard and write to file
while (1)
{
// prompt user
printf("\nFirst Name: ");
scanf ("%s", input.fname);
// exit if no name provided
if (strcmp(input.fname, "stop") == 0)
exit(1);
// continue reading from keyboard
printf("Last Name : ");
scanf ("%s", input.lname);
printf("Acct Num : ");
scanf ("%d", &input.acct_num);
printf("Balance : ");
scanf ("%f", &input.acct_balance);
// write entire structure to Accounts file
fwrite (&input, sizeof(struct customer), 1, outfile);
}
FILE *infile;
/*** open the accounts file ***/
infile = fopen ("C:\\Users\\Admin\\Desktop\\read\\per.dat","r");
if (infile == NULL)
{
fprintf(stderr, "\nError opening accounts.dat\n\n");
exit (1);
}
while (fread (&input, sizeof(struct customer), 1, infile))
printf ("Name = %10s %10s Acct Num = %8d Balance = %8.2f\n",
input.fname, input.lname, input.acct_num, input.acct_balance);
}
when I input info into the program, it just writes random characters in file .dat and doesn't show the info I have written. Please help me to find the problem of that.

Answer 1

You have:
if (strcmp(input.fname, "stop") == 0)
exit(1);
This ends your program at that point. I don't think you want that. Rather, break your loop:
if (strcmp(input.fname, "stop") == 0)
break;
Also, be sure to close your file after you're done writing to it and before you open it for reading. Otherwise, it may not exist or output to it may not be flushed:
fclose(outfile);
Finally, note that fwrite() will write the binary data of your struct. This will look like garbage to the human eye, even though fread() should read it correctly. But note that you should open the file as binary both for reading and for writing. Otherwise, some systems (Windows, at least) will do some interpreting of the data.
outfile = fopen ("C:\\Users\\Admin\\Desktop\\read\\per.dat","wb");
infile = fopen ("C:\\Users\\Admin\\Desktop\\read\\per.dat","rb");
With those changes, your code seems to work fine for me.
Be aware that writing and reading binary data in this way can be fraught with peril if you are using different platforms for writing and reading, sending data over a network, or potentially even using different compile options. Byte ordering ("endianness"), data type sizes, and structure padding can all cause you problems. For real-world problems, some kind of portable serialization would be better.