Reading and writing binary data structures
The fread() function reads an indicated number of elements,
each of which is the same size:
size_t fread(void *ptr, size_t eachsize, size_t nelem, FILE *stream);
This mechanism enables our programs to read arbitrary sized data,
by setting eachsize to one (a single byte),
or to read a known number of data items each of the same size:
#include <stdio.h>
int intarray[ N_ELEMENTS ];
int got, wrote;
// OPEN THE BINARY FILE FOR READING AND WRITING
FILE *fp = fopen(filename, "rb+");
....
got = fread( intarray, sizeof int, N_ELEMENTS, fp);
printf("just read in %i ints\n", got);
// MODIFY THE BINARY DATA IN THE ARRAY
....
// REWIND THE FILE TO ITS BEGINNING
rewind(fp);
// AND NOW OVER-WRITE THE BEGINNING DATA
wrote = fwrite( intarray, sizeof int, N_ELEMENTS, fp);
....
fclose(fp);
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CITS2002 Systems Programming, Lecture 7, p14, 12th August 2024.
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CITS2002