Infinitely reading input when inputting a file from stdin - c

Question

I want to parse information from a CSV file and display it to my screen. My issue is that I keep receiving Segmentation fault core dumped from my while loop, which is supposed to be storing the CSV file info into different arrays to represent the different columns in the CSV. A sample line in my CSV would be rice,10,20,$2.00 which represents the food, stock, reorder limit, and cost per unit.
char buffer[1024];
char *line=buffer;
FILE *file=fopen("inventory.csv", "rw");
int x;
int i=0;
int j=0;
char *food [100];
int stock [100];
double cost [100];
int reorder [100];
while (fgets(line, 2048, file) != NULL){
food[i] = (strtok(line, ","));
stock [i] = (atoi(strtok(NULL, ",")));
reorder[i] = (atoi(strtok(NULL, ",")));
cost[i] = (atof(strtok(NULL, ",")));
line=line+25;
i++; }

Answer 1

First, your code has a basic problem: you want to read an infinite amount of data and store it into finite space.
In more details:
You keep advancing line by 25 after each line, it points to buffer which has a size of 1024, so after 40 lines you will be writing after the end of it.
Your arrays have a size of 100, so after 100 lines you will be writing after the end of them.
Do you need to store everything you read forever?
Now if this is not the problem, it could also be that strtok fails to find the "," and returns NULL, you should always check the return of strtok before using the result. It may for example fail if your file finishes with some empty lines, or just that you don't have a "," after the last element of the line that you read.

Answer 2

My bet is that you're trying to access a position in your arrays that doesn't exist. Try looking the last i value before your program crashes.

Answer 3

Please take a look at the following class. You may call it with
main.cpp
Stock line_stock;
file >> line_stock; //Use it in a loop cause it only reads a line
Stock.h
#include <iostream>
#include <string>
class Stock {
public:
private:
std::string food;
unsigned int stock;
double cost;
unsigned int reorder;
friend std::istream& operator >> (std::istream& is, Stock& s){
char coma;
is >> s.food >> coma>>
s.stock >> coma >>
s.cost >> coma >>
s.reorder;
return is;
}
};
//double doesn't work well on money, use unsigned int instead. Divide by 100 to get the dollar and % 100 to get the cents.
Using that class reads a line, then you process it and you're up to the next line.

Answer 4

When trying to read a file with an unknown number of data lines 2 approaches come to mind:
1) Read line by line and adjust memory allocation as needed.
2) Parse the file twice. First to find needed length.
A robust program typically uses method #1. But #2 is simpler for learners. #2 follows.
FILE *file = fopen("inventory.csv", "rw");
// Test for file == NULL
char buffer[100];
size_t n = 0;
// Find number of lines
while (fgets(buffer, sizeof buffer, file) != NULL)
n++;
char *food = malloc(n * sizeof *food);
int stock = malloc(n * sizeof *stock);
double *cost = malloc(n * sizeof *cost);
int *reorder = malloc(n * sizeof *reorder);
// TBD: Add checks for failed malloc
rewind(file);
size_t i = 0;
for (i = 0; i<n; i++) {
char name[sizeof buffer];
if (fgets(buffer, sizeof buffer, file) != NULL) Handle_UnexpectedError();
int cnt = sscanf(buffer, "%s ,%d ,%d , $%lf",
name, &stock[i], &reorder[i], &cost[i]);
if (cnt != 4) Handle_FormatError();
food[i] = strdup(name);
}
fclose(file);
// Use food, stock, reorder, cost
// When done
for (i = 0; i<n; i++) {
free(food[i]);
}
free(food);
free(stock);
free(reorder);
free(cost);