Loading data from a file to an array in c - c

Question

I want to load an array from a file that I previously saved. I ran the code below, but for some reason, when I loaded the array, the array length that I loaded was not the same as the length of the array that I had saved. How would I change the length for my load a file code so that it would work for any array length?
intarr_t* intarr_load_binary( const char* filename )
{
unsigned int len = 0;
FILE *f = fopen (filename, "rb");
fscanf (f, "%d", len);
intarr_t* newia = malloc (sizeof(intarr_t));
assert (newia);
newia->data = malloc (len*sizeof(int));
assert(newia->data);
newia->len = len;
if (f != NULL)
{
while (!feof(f))
{
fscanf (f, "%d", newia->data);
}
}
else
{
return NULL;
}
fclose (f);
return newia;
}
The struct that I used for the save/load is here:
typedef struct {
int* data;
unsigned int len;
} intarr_t;
The code that I used to save the file is here:
int intarr_save_binary( intarr_t* ia, const char* filename )
{
unsigned int len = ia->len;
FILE *f;
f = fopen (filename, "wb");
if (fwrite (ia->data, sizeof(int), len, f) == len)
{
return 0;
}
else
{
return 1;
}
fclose (f);
}

Answer 1

the code is writing no length (len) value as the first data item to the file
yet the code is reading a length (len) value
as if it were the first data item in the file.
this code is full of errors and oversights:
int intarr_save_binary( intarr_t* ia, const char* filename )
{
unsigned int len = ia->len;
FILE *f;
f = fopen (filename, "wb");
if (fwrite (ia->data, sizeof(int), len, f) == len)
{
return 0;
}
else
{
return 1;
}
fclose (f);
}
suggest using code similar to this:
int intarr_save_binary( intarr_t* ia, const char* filename )
{
int returnValue = 0;
unsigned int len = ia->len;
FILE *f;
if( NULL == (f = fopen (filename, "wb") )
{
perror( "fopen failed" );
returnValue = 1;
}
else if ( fwrite ( &len, sizeof(int), 1, f) == 1 )
{ // then write of length successful
if (fwrite (ia->data, sizeof(int), len, f) == len)
{
returnValue = 0; // indicate success
}
else
{ // else, write of data failed
returnValue = 3;
}
}
else
{ // else, failed to write len value to file
returnValue = 4;
}
fclose( f ); // cleanup (writes last buffer to file)
return( returnValue );
} // end function: intarr_save_binary

Answer 2

this code needs some work.
for instance because assert should not enabled in production code
and error conditions not being checked
and cleanup not being properly performed
if the program is ok to continue after an I/O error
by always returning NULL
then you could change the following,
to return NULL rather than exiting the program
intarr_t* intarr_load_binary( const char* filename )
{
unsigned int len = 0;
FILE *f = fopen (filename, "rb");
fscanf (f, "%d", len);
intarr_t* newia = malloc (sizeof(intarr_t));
assert (newia);
newia->data = malloc (len*sizeof(int));
assert(newia->data);
newia->len = len;
if (f != NULL)
{
while (!feof(f))
{
fscanf (f, "%d", newia->data);
}
}
else
{
return NULL;
}
fclose (f);
return newia;
}
suggest:
intarr_t* intarr_load_binary( const char* filename )
{
unsigned int len = 0;
FILE *f = NULL;
intarr_t* newia = NULL;
if( NULL == fopen (filename, "rb") )
{ // then, fopen failed
perror( "fopen failed" );
exit( EXIT_FAILURE );
} // end if
// implied else, fopen successful
if( NULL == (newia = malloc (sizeof(intarr_t)) )
{ // then malloc failed
perror( "malloc failed" );
fclose(f);
exit( EXIT_FAILURE );
} // end if
// implied else, malloc successful
if( (fread (&len, sizeof(int), 1, f) != 1 ) )
{ // then fread failed
perror( "fread failed" );
fclose(f);
free( newia );
exit( EXIT_FAILURE );
} // end if
// implied else, fread for len successful
newis->len = len;
if( NULL == (newia->data = malloc (len*sizeof(int)) ) )
{ // then malloc failed
perror( "malloc failed" );
fclose(f);
free( newia );
exit( EXIT_FAILURE );
} // end if
// implied else, malloc successful
if( fread( newia->data, sizeof(int), len, f ) != len )
{ // then, fread failed
perror( "fread failed" );
fclose(f);
free(newia->data)l
free(newia);
exit( EXIT_FAILURE );
} // end if
// implied else, fread successful
fclose (f);
return newia;
} // end function: intarr_load_binary