Segmentation fault with File I/O 1

[GoAskAlice]

Basically, I am learning C under Linux. What I am attempting is fwrite and fread functions on a file.

The write program works without fault, but when I try and read the data back from the file, the data is displayed, but then at the end of it all it states 'Segmentation fault'.

So, here is the code...can anyone help?

write file.c
----------------------------------------------------------
// Write to file using fwrite

#include <stdio.h>

int main() {
FILE *fp;
int writecount = 0;
int a[4];
a[0] = 12345678;
a[1] = 23456789;
a[2] = 34567891;
a[3] = 45678912;
if (( fp = fopen( "items.txt", "w" )) == NULL ){
perror ( "Opening data file" ); return -1;
}
writecount = fwrite( a, sizeof (a), 8, fp );




if ( fclose(fp) != 0)
{
fprintf(stderr, "Error closing file.\n");
return -2;
}
return 0;
}
----------------------------------------------------------



read file.c
-----------------------------------------------------------
// Read file using fread

#include <stdio.h>

int main() {
FILE *fp;
int a[4];
int readcount = 0;
int c;

if (( fp = fopen( "items.txt", "r+" )) == NULL){
perror( "Opening data file" );
return -1;
}

readcount = fread( a, sizeof( a ), 8, fp);

for( c = 0; c < 4; c++ ) {
printf("%i\n",a[c]);
}

if ( fclose(fp) != 0)
{
fprintf(stderr, "Error closing file.\n");
return -2;
}
return 0;
}
-----------------------------------------------------------

 

[GoAskAlice]

No worries, I figured it out.

The problem was with the fread() function.

Basically, I was asking it to read 8 times the data inside the array 'a'.

So, like,

instead of;
readcount = fread( a, sizeof( a ), 8, fp);

I used;
readcount = fread( a, sizeof( a ), 1, fp);

And this extracted all the data without the Segmentation Fault.

 

[cpjust]

You have the same problem with fwrite().

 

[maur3r]

I suggest another way.

/*WRITING TO FILE*/

#include <stdio.h>

int main() {
FILE *fp;
int writecount = 0;
int a[4];
int size, i/*in loop*/;
/*if you don't know actual array size you can always check it*/
/*size=sizeof(a)/sizeof(a[0]);*/
/*but we know it's 4*/
size=4;
a[0] = 12345678;
a[1] = 23456789;
a[2] = 34567891;
a[3] = 45678912;
if (( fp = fopen( "items", "w" )) == NULL ){
    perror ( "Opening data file" ); return -1;
}
for (i=0; i<size; i++){
writecount=fprintf(fp,"%d \n",a[i]);
 if(writecount<0){
  perror("Error writing to a file");
  return -1;
}
}


if ( fclose(fp) != 0)
{
    fprintf(stderr, "Error closing file.\n");
    return -2;
}
return 0;
}

/*READING FROM FILE*/

#include <stdio.h>

int main() {
FILE *fp;
int writecount = 0;
int a[4];
int numberOfObjects=4	, i/*in loop*/;
if (( fp = fopen( "items", "r" )) == NULL ){
    perror ( "Opening data file" ); return -1;
}
for (i=0; i<numberOfObjects; i++){
writecount=fscanf(fp,"%d",&a[i]);
 if(writecount<0){
  perror("Error writing to a file");
  return -1;
}
}

for (i=0; i<numberOfObjects; i++)
printf("%d \n",a[i]);

if ( fclose(fp) != 0)
{
    fprintf(stderr, "Error closing file.\n");
    return -2;
}
return 0;
}

Hope it will be useful for you.