seg fault in c with pointers - c

Question

I have two fucntions that prompt the user to print ingredients names for pizza and print them out. But whenever I'm trying to print out the available ingredients, I get a seg fault.
And when I prompt to enter ingredients, if I say we have 3 available ingredients today, I can only type 2 in (as shown in the output picture)
int get_ingredients(char** ingredients,int* num_ingredients) {
char **ingredients_array = NULL; /*this is an array of pointers points to single ingredient in get_item*/
int temp,i,j;
ingredients = &ingredients_array; /*ingredients is a pointer points to the array of pointers*/
temp = *num_ingredients;
printf("How many available pizza ingredients do we have today? ");
scanf("%d",&temp);
ingredients_array = (char**)calloc(temp, sizeof(char*));
i = 0;
printf("Enter the ingredients one to a line: \n");
while (i < temp){
*(ingredients_array+i) = get_item();
i++;
}
i = 0;
printf("Available ingredients today are: \n");
while(i < temp) {
j = i+1;
printf("%d",j);
print(". ");
printf("%s", **(ingredients_array+i));
i++;
}
*num_ingredients = temp;
return EXIT_SUCCESS;
}
char* get_item(){
int i,a;
char *each_ingredient= (char*)malloc(61*sizeof(char)); /*points to each input*/
a = getchar();
i = 0;
while (a != EOF && (char)a != '\n'){
*(each_ingredient+i)= (char)a;
a = getchar();
i++;
}
*(each_ingredient+i) = '\n';
return each_ingredient;
}
This is the output

Answer 1

There are many issues with your get_ingredients question.
The first issue that I noticed is that you changed the pointer of the parameter ingredients, you changed it to the pointer get_ingredients which was set to NULL. So accessing the data from ingredients pointer from now on will get you a segmentation fault, for trying to access an illegal address.
int get_ingredients(char** ingredients,int* num_ingredients) {
char **ingredients_array = NULL; /*this is an array of pointers points to single ingredient in get_item*/
int temp,i,j;
//ingredients pointer is lost forever and set to the address of the pointer of ingredients_array
ingredients = &ingredients_array; /*ingredients is a pointer points to the array of pointers*/
Now the second issue is more of an optimization thing. You set a variable, and then you changed it on the scanf, making the useless to set it to some value initially.
//Temp is set to num_ingredients, but this is of no use,becuase this value is never used and is overwritten by scanf("%d",&temp);
temp = *num_ingredients;
printf("How many available pizza ingredients do we have today? ");
scanf("%d",&temp);
Should allocate pointer of a pointer to char.
ingredients_array = (char**)calloc(temp, sizeof(char*));
Changes
ingredients_array = (char**)calloc(temp, sizeof(char**));
The while loops can be replaced with a for a loop. Which a more appropriate type of loop for this case.
//This can write it better with a for loop
i = 0;
printf("Enter the ingredients one to a line: \n");
while (i < temp){
*(ingredients_array+i) = get_item();
i++;
}
i = 0;
printf("Available ingredients today are: \n");
//Use for loop intead, because it more appropiate for this case
while(i < temp) {
//better to use i+1 instead of j, simply things
j = i+1;
//These two printf can be on the same line
printf("%d",j);
printf(". ");
//Allocation error?
printf("%s", **(ingredients_array+i));
i++;
}
Using a for loop instead, getting user input from standard function, and using less confusing indexing.
printf("Enter the ingredients one to a line: \n");
//Using for loop
for(int i = 0;i < temp;i++)
{
char ptr[80]; //Store user input
scanf("%s", ptr); //Get user input
ingredients_array[i] = strdup(ptr); //strdup is to make a another string with the same contents
}
printf("Available ingredients today are: \n");
for(int i = 0; i < temp;i++)
{
//These two printf can be on the same line
printf("%d",i+1);
print(". ");
//Allocation error?
printf("%s\n", ingredients_array[i]);
}
*num_ingredients lost its original pointer earlier, so this serves no use.
//This cannot be used because now points to ingredients_array and not to num_ingredients
*num_ingredients = temp;
Now the code with all those changes.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int get_ingredients(char** ingredients,int* num_ingredients) {
char **ingredients_array = NULL; /*this is an array of pointers points to single ingredient in get_item*/
int temp;
printf("How many available pizza ingredients do we have today? ");
scanf("%d",&temp);
ingredients_array = (char**)calloc(temp, sizeof(char**));
printf("Enter the ingredients one to a line: \n");
//Using for loop
for(int i = 0;i < temp;i++)
{
char ptr[80]; //Store user input
scanf("%s", ptr); //Get user input
ingredients_array[i] = strdup(ptr); //strdup is to make a another string with the same contents
}
printf("Available ingredients today are: \n");
for(int i = 0; i < temp;i++)
{
printf("%d. ",i+1);
printf("%s\n", ingredients_array[i]);
}
*num_ingredients = temp;
return EXIT_SUCCESS;
}
int main()
{
char** ingredients;
int a;
int foo = get_ingredients(ingredients, &a);
return 0;
}
Output
How many available pizza ingredients do we have today? 4
Enter the ingredients one to a line:
meat
MEAT
mEaT
no_salas
Available ingredients today are:
1. meat
2. MEAT
3. mEaT
4. no_salad