Fscanf Seg Error - c

Question

Working on a project where I have to have a file that is generated numbers. First line is a generated int. Followed by a floats (separate lines). (I'm doing it separate lines because I feel it makes more sense as I have to read it two different ways for the bin packing problems which I need this for... Like one way of reading one at a time and another storing it in an array.. But want to get this down first)
Getting a seg fault when I try to read my file for a float after reading an int. Edit: Error occurs in readOffline.
int randomFunction()
{
FILE *fp;
int i;
fp = fopen("theItems.txt", "w" );
if (fp == NULL)
printf("Error: file can't be opened.\n");
srand(time(NULL) );
int random_number = rand();
printf("Random Number %d\n", random_number);
fprintf(fp,"%d",random_number);
fclose(fp);
fp = fopen("theItems.txt", "a");
int numberOfItems = rand();
printf("NumberOfItems: %d\n",numberOfItems);
for(i = 0; i < 10; i++)
{
fp = fopen("theItems.txt", "a");
float number = (float)rand()/(float)(RAND_MAX);
fprintf(fp,"%f",number);
fprintf(fp,"%s", "\n");
fclose(fp);
}
return numberOfItems;
}
void readOffline( int numberOfItems)
{
FILE *fp;
int n = 0,i;
float nu = 0.00;
fp = fopen("theItems.txt", "r");
if (fp == NULL)
printf("Error: file can't be opened.\n");
fseek(fp,SEEK_SET,0);
fscanf(fp,"%d",&n);
printf("Number read: %d\n", n);
float array[numberOfItems];
// for(i = 0; i < 3; i++)
// {
fscanf(fp,"%f",&nu);
// array[i] = nu;
// }
fclose(fp);
printf("Int:%d\n", n);
int j;
// for(j = 0; j < 3; j++)
// printf("Float Number:%f\n", array[j]);
}
int main()
{
int numberOfItems = randomFunction();
readOffline(numberOfItems);
return 0;
}
Just trying to get an understanding why it causes a seg error when I // it out I can get it to read my int but sometimes it isn't the right int read. But yeah.
Please let me know if I need any more details or need to be more clear anywhere

Answer 1

You have multiple issues in your code:
You open the output file multiple times in randomFunction(), you even leak a stream handle and leave it open.
You do not exit the function when fopen() returns NULL. The rest of the code invokes undefined behavior if fp == NULL.
The same problem is present in readOffline(): if fp == NULL, you should return from the function immediately.
you do not output a linefeed after the first random number in the output file.
you always output 10 random numbers.
most importantly: the random number returned by the randomFunction() is potentially huge, allocating an array with local storage larger than a few megabytes is likely to cause undefined behavior. Try and reduce the maximum random number of values.
Here is a proposed correction:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int randomFunction(void) {
FILE *fp;
int i;
fp = fopen("theItems.txt", "w");
if (fp == NULL) {
printf("Error: file can't be opened.\n");
return -1;
}
srand(time(NULL));
int random_number = rand();
printf("Random Number %d\n", random_number);
fprintf(fp, "%d\n", random_number);
int numberOfItems = 1 + rand() % 100; /* between 1 and 100 */
printf("NumberOfItems: %d\n", numberOfItems);
for (i = 0; i < numberOfItems; i++) {
float number = rand() / (float)(RAND_MAX);
fprintf(fp, "%f\n", number);
}
fclose(fp);
return numberOfItems;
}
void readOffline(int numberOfItems) {
FILE *fp;
int n = 0, i;
fp = fopen("theItems.txt", "r");
if (fp == NULL) {
printf("Error: file can't be opened.\n");
return;
}
fscanf(fp, "%d", &n);
printf("Number read: %d\n", n);
float array[numberOfItems];
for (i = 0; i < numberOfItems; i++) {
if (fscanf(fp, "%f", &array[i]) != 1)
break;
}
fclose(fp);
printf("Int:%d\n", n);
for (int j = 0; j < i; j++) {
printf("Float Number %d: %f\n", j, array[j]);
}
}
int main(void) {
int numberOfItems = randomFunction();
readOffline(numberOfItems);
return 0;
}
Note that I kept your semantics: the random number at the start of the file is not the number of floating point values that follow. I suspect it should be?

Answer 2

I would say that depending on the particular compiler that you are using, then this could be a problem in setting up the actual array. This is (as an example) discussed in Variable Sized Arrays vs calloc in C From the discussions, you should use calloc and free. Another point is that you need to make sure that your value is greater than 3 and not too big. Since the array is only in the local scope of readOffline(), you should not connect it to the variable numberOfItems.
float array[3];
for(i = 0; i < 3; i++)
{
fscanf(fp,"%f",&nu);
array[i] = nu;
}