reading from a file to make an array using C [closed] - c

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Closed 9 years ago.
How do I make an array by reading from a .txt file??
I'm making a bidding(auction) program. I need to read integers from the .txt and use those in an array. I am confused as to how I would go about that in my program.
The txt is as follows:
100 15
200 20
300 25
400 30
500 35

Answer 1

It is definitely recommended to show one's own effort while asking the question. However, to give you a jump start, please find a couple of solutions as below.
One possible illustrative solution using a static array is as in Solution 1 below. The assumption in the solution below is that the number of elements is known and is less than 32. If wish to keep it truly dynamic, you will have to implement a solution using a linked list as in Solution 2 below.
Solution 1: Fixed Array based approach
int main()
{
FILE *finp;
int someArr[32];
int i, ctr = 0;
finp = fopen("haha.txt", "r");
if(NULL == finp)
{
printf("Unable to open file\n");
exit(-1);
}
while((!feof(finp)) && (ctr < 32))
{
fscanf(finp, "%d ", &someArr[ctr++]);
}
for(i = 0; i < (ctr -1); i++)
{
printf("%d==>", someArr[i]);
}
printf("%d\n", someArr[i]);
fclose(finp); //Close the file pointer
return 0;
}
The expected output of this program is
100==>15==>200==>20==>300==>25==>400==>30==>500==>35
Solution 2: Linked List based solution
Further to my earlier comment, please find an alternative dynamic solution which doesn't require a prior knowledge on the number of elements as below.
typedef struct node {
int value;
struct node *next;
}node;
void createList(FILE *fInp, node **headBase)
{
node *currNode;
node *head = *headBase;
node *tail;
while(!feof(fInp))
{
currNode = malloc(sizeof(struct node));
fscanf(fInp, "%d ", &currNode->value);
currNode->next = NULL;
if(NULL == head)
{
head = currNode;
tail = currNode;
}
else
{
tail->next = currNode;
tail = currNode;
}
}
//Store back the updated head pointer
*headBase = head;
}
void printList(node **headBase)
{
node *tmpNode = *headBase;
while(tmpNode->next != NULL)
{
printf("%d-->", tmpNode->value);
tmpNode = tmpNode->next;
}
printf("%d\n", tmpNode->value);
}
void deleteList(node **headBase)
{
node *head = *headBase;
node *tmp;
while(NULL != head)
{
tmp = head; // Get a temp pointer
head = head->next; // Move head pointer
tmp->next = NULL; // break the link
printf("<< Deleted Node: %d\n", tmp->value);
free(tmp);
}
// Store the head pointer back which should be NULL
*headBase = head;
}
int main()
{
FILE *finp;
node *head = NULL;
finp = fopen("haha.txt", "r");
if(NULL == finp)
{
printf("Unable to open file\n");
exit(-1);
}
createList(finp, &head);
printList(&head);
deleteList(&head);
fclose(finp);
return 0;
}
The expected output of this program is
100-->15-->200-->20-->300-->25-->400-->30-->500-->35
<< Deleted Node: 100
<< Deleted Node: 15
<< Deleted Node: 200
<< Deleted Node: 20
<< Deleted Node: 300
<< Deleted Node: 25
<< Deleted Node: 400
<< Deleted Node: 30
<< Deleted Node: 500
<< Deleted Node: 35

Answer 2

Supposing you don't know how many integers can be found in the input file, you could define a max value.
You must too include stdio.h and stdlib.h
#define MAX 255
int main() {
FILE *file = fopen("input.txt", "r");
int integers[MAX];
int i = 0;
if (file != NULL) {
while (!feof(file) && i < MAX) {
if (fscanf(file, "%d", &integers[i++]) != -1) {
printf("%d ", integers[i-1]);
}
}
fclose(file);
} else {
printf("Unable to open file");
return EXIT_FAILURE;
}
return 0;
}