How can I fill a string variable-sized array? - c

Question

I need to build an Coin Dispenser application. I've written the withdrawal and deposit parts but in item inventory creation I couldn't create a solution to that. Item names should be taken from keyboard as strings. Item prices corresponding to the items should be taken from keyboard as unsigned ints.
Arrays should be variable-sized, aka VLAs. I've googled it and found some resources about creating VLAs, I think I should allocate memory to them dynamically using malloc. I couldn't do that, so I basically created limited sized arrays with using BUFSIZ.
How can I use VLAs in this case, and how can I fill them with strings?
Also I should prevent buffer overrun. This will be the second case.
Macros and code blocks:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define NUMBER_OF_COINS 5
#define ITEM_NAME_LEN 9
...
void editorMain(void)
{
printf("Please enter the number of items: ");
scanf("%u", &itemQuantity);
printf("\n\n");
char ** itemNames[BUFSIZ] = {0};
unsigned int itemPrices[BUFSIZ] = {0};
printf("Please enter the names of items: \n");
for (int i = 0; i < itemQuantity; ++i) {
printf("#%d: ", i + 1);
gets(** itemNames[i]);
puts("");
}
printf("Please enter the prices of items: \n");
for (int i = 0; i < itemQuantity; ++i) {
printf("#%d: ", i + 1);
scanf("%u", &itemPrices[i]);
puts("");
}
dispenserMain(*itemNames, itemPrices);
return;
}
Also program should output the item names and prices as a list. Function dispenserMain does this:
void dispenserMain(char * itemNames[], unsigned int itemPrices[]) {
...
for (counterItemNames = 1; counterItemNames <= itemQuantity; ++counterItemNames) { //the for loop will print out the item name and prices with their correspondence.
printf("%10u.%14s%12.2f TL\n", counterItemNames, itemNames[counterItemNames - 1], currencyConverter(itemPrices[counterItemNames - 1]));
}
...
}
Edit (new code):
void editorMain(void)
{
printf("Please enter the number of items: ");
scanf("%u", &itemQuantity);
printf("\n\n");
char itemNames[itemQuantity][ITEM_NAME_LEN+1];
memset(&itemNames, 0, sizeof(itemNames));
printf("Please enter the names of items: \n");
char line[ITEM_NAME_LEN+1];
for (int i = 0; i < itemQuantity; ++i) {
printf("#%d: ", i + 1);
if (! fgets(line, sizeof(line), stdin) || !line[0])
// abort...
// fgets leaves the trailing newline in the input
if (line[strlen(line)-1] == '\n') {
line[strlen(line)-1] = 0;
}
snprintf(itemNames[i], ITEM_NAME_LEN+1, "%s", line);
puts("");
}
unsigned int itemPrices[] = {0};
printf("Please enter the prices of items: \n");
for (int i = 0; i < itemQuantity; ++i) {
printf("#%d: ", i + 1);
scanf("%u", &itemPrices[i]);
puts("");
}
dispenserMain(itemNames, itemPrices);
return;
} //end globalMenuOut
It outputs:
Welcome to CoinedDispenser!
Author: Buğra Ekuklu
Contact: bugraekuklu [at] hotmail.de
1. Dispenser
2. Editing variables
3. Readme
Please make a choice: 2
Please enter the number of items: 3
Please enter the names of items:
#1:
#2: blabla
#3: glagla
Please enter the prices of items:
#1: 45
#2: 65
#3: 75
................... AVAILABLE ITEMS oo
# Item Name Price
= ========= ======
1.
0.45 TL
2. blabla
0.65 TL
3. glagla
0.75 TL
Enter your item selection:
Dispenser function:
void dispenserMain(char (*itemNames)[ITEM_NAME_LEN+1], unsigned int itemPrices[])
{
printf("%s\n\n", " ................... AVAILABLE ITEMS oo");
printf("%10s%15s %14s\n", "#", "Item Name", "Price");
printf("%10s%15s %14s\n", "=", "=========", "======");
puts("");
unsigned int counterItemNames = 0; //initializing counter
for (counterItemNames = 1; counterItemNames <= itemQuantity; ++counterItemNames) { //the for loop will be print out the item name and prices with their correspondence.
printf("%10u.%12s%12.2f TL\n", counterItemNames, itemNames[counterItemNames - 1], currencyConverter(itemPrices[counterItemNames - 1]));
}
puts("");
...
}

Answer 1

Where you write char ** itemNames[BUFSIZ] = {0}; should be:
char itemNames[itemQuantity][ITEM_NAME_LEN+1];
This is a VLA because it has an array that has a dimension known at
runtime. Space allocated via malloc is not a VLA.
Unfortunately VLAs cannot have initializers, so you would also have
to write:
memset(&itemNames, 0, sizeof itemNames);
If you want to dynamically allocate this array it would be:
char (*itemNames)[ITEM_NAME_LEN+1];
itemNames = calloc( itemQuantity, sizeof *itemNames );
and in both cases the usage will be identical. itemNames[i] designates an array which you have allocated.
Your code gets(** itemNames[i]); has two problems; it dereferences a null pointer, and it uses the gets function which allows the user to cause a buffer overflow. You should be reading into the array itemNames[i], which after using my suggestion above, designates storage you've allocated.
Unfortunately it's awkward in C to just input a string of fixed length. You have to worry about what happens if the user types more than your line length. If that doesn't concern you too much then:
char line[BUFSIZ];
if ( ! fgets(line, sizeof line, stdin) || !line[0] )
// abort...
// fgets leaves the trailing newline in the input
if ( line[strlen(line)-1] == '\n' )
line[strlen(line)-1] = 0;
snprintf(itemNames[i], ITEM_NAME_LEN+1, "%s", line);
To call your function do:
dispenserMain(itemNames, itemPrices);
and the function has to be
void dispenserMain(char (*itemNames)[ITEM_NAME_LEN+1], unsigned int itemPrices[]);
If you want to use your original the syntax for dispenserMain then you have to allocate an array of pointers, as opposed to using a 2-D array as I have described. In that case you would use char **itemNames = malloc(itemQuantity * sizeof *itemNames); and the loop through and malloc each pointer to point to some more storage of length ITEM_NAME_LEN+1.