Please help a student!

[Valistar]

I am learning C++ and it's giving me problems

For one of my assignments I need to input data from a binary file containing structs that the user inputs info to.

I can create the file no worries it when i try to read them back from the file into the program that I have problems. I am supposed to be randomly accessing the file (no sequential searches) based on input from the user, then displaying the info to the user.
If anyone can help I would really appreciate it.

Help me [insert name] youre my only hope!!

 

[victorv]

Hi,

the fastets way to access bynary data from file is
to use the same structure type from routines that writes
and reads data. For this purpose you have to write 2 routines (or 2 programs: 1 writes , 1 reads ).

mystruct.h
----------
stuct mystruct {
char c;
int i ; }

write.c
-------
#include "mystruc.h"
FILE *stream;
struct mystruct s ;
s.c='A';
s.i=0;
.....
stream=fopen( "myfile.dat", "w+b" ) ; // see doc about +b
fwrite( &s, sizeof(s), 1, stream ) ;
fclose(stream);

read.c
-------
#include "mystruc.h"
FILE *stream;
struct mystruct s ;
.....

stream=fopen( "myfile.dat", "r+b" ) ; // see doc about +b
fread( &s, sizeof(s), 1, stream ) ;
fclose(stream);

printf( "%c %d\n", s.c, s.i ) ;

******* *******

Using this method is very fast, by I suggest another way.
I work with programs from more that 20 years: this method is
fast but you have to manage 2 programs and to see data on
file, you need a your-written program: during debug you don't know if the error is in the program 1 or 2.

Using text file, for store data, is longer: to save
data you have to use printf and scanf to retrieve.
But you can print file.dat directly or consult it
by an editor: if you are the alone user, you can
omit to write the writing program: you can use text-editor.

If you, however, intend to use binary file warning to a thing: the compiler may put the fileds not near each to other; to optimize int access, it can leave 1 or 3 bytes
between c and i (see mystruct); if you use the same compiler
and CPU to build write and read there are no problem.
Put attention ti the file size: it can be 3 bytes long
4 or 8, depending size of int and the type of alligment.

bye.