Reading file using fscanf is not working in c? - c

Question

int main(int argc, char **argv) {
char *input = "input.txt";
int *account;
char **name;
float *balance;
int count;
int check;
if (argc < 4 || argc > 4) {
printf("Insufficient arguments. Check your command line arguments\n");
return 1;
}
count = atoi(*(argv + 2));
name = malloc(sizeof(char) * 20 * count);
account = malloc(sizeof(int) * count);
balance = malloc(sizeof(float) * count);
check = load_data(input, name, account, balance, count);
if (check == 0) {
printf("File cannot be open\n");
}
print_data(name, account, balance, count);
free(name);
return 0;
}
//load data from input file the according arrays
int load_data(char *input, char **name, int *acct, float *amt, int n) {
int *a = acct;
float *b = amt;
FILE *file = fopen("input.txt", "r");
int i;
if (file == NULL) {
return 0;
} else {
for (i = 0; i < 9; i++, acct++, amt++) {
fscanf(file, "%s %d %f", *(name + i), acct, amt);
}
}
fclose(file);
acct = a; //return pointer to original position
amt = b;
return 1;
}
//print data from arrays
void print_data(char **name, int *acct, float *amt, int n) {
int i;
for (i = 0; i < n; i++) {
printf("%-10s%-13s%s\n", "Name", "Account No.", "Amount");
printf("%-10s%-13d%7.2f\n", *(name + i), *(acct + i), *(amt + i));
}
}
I have this load_data function that suppose to read from a file and store the data values in different pointers, but for some reason when I print out using print_data function, the pointer contain all null and 0? (Please answer using pointers arithmetic and not array)

Answer 1

I expect that you have not properly prepared the arrays before calling the function... the below main function will work with your code:
int main(int argc, char* argv[]) {
int n = 10;
char ** name = malloc(n * sizeof(char*));
int* acct = malloc(n * sizeof(int));
float* amt = malloc(n * sizeof(float));
for (int i = 0; i < n; i++) {
// this is allocating some space for each line
// this is quite bad you should range check.
name[i] = malloc(256);
}
load_data("", name, acct, amt, n);
print_data(name, acct, amt, n);
// TODO: free everything
}
in load_data: a and b are not required and as amt and acct are "passed by value" there is no need to restore their values at the end of your function. That is to say that the values in all your arguments will be discarded when this function returns only the values that are "pointed to" are updated.
Example input.txt file:
Adam 1 900.9
Daniel 2 800.8
Joe 3 700.7
Foo 4 600.6
Bar 5 500.5
Alice 6 400.4
Bob 7 300.3
Nick 8 200.2
Eve 9 100.1
After altering your code slightly (see below) the above input file does work, here is the output I get:
$ ./test 5 5 5
Name Account No. Amount
Adam 1 900.90
Name Account No. Amount
Daniel 2 800.80
Name Account No. Amount
Joe 3 700.70
Name Account No. Amount
Foo 4 600.60
Name Account No. Amount
Bar 5 500.50
Updated main function based on the one you provided in the question:
int main(int argc, char **argv) {
char *input = "input.txt";
int *account;
char **name;
float *balance;
int count;
int check;
int i;
if (argc < 4 || argc > 4) {
printf("Insufficient arguments. Check your command line arguments\n");
return 1;
}
count = atoi(*(argv + 2));
name = malloc(sizeof(char *) * count);
for (i = 0; i < count; i ++) {
*(name+i) = malloc(20);
}
account = malloc(sizeof(int) * count);
balance = malloc(sizeof(float) * count);
check = load_data(input, name, account, balance, count);
if (check == 0) {
printf("File cannot be open\n");
}
print_data(name, account, balance, count);
free(balance);
free(account);
for (i = 0; i < count; i++) {
free(*(name+i));
}
free(name);
return 0;
}
... also in load_data I changed i < 9 to i < n.