CODEWITHSUNDEEP
carraysstringpointers
Alejandro Zapien
Alejandro Zapien

Reputation: 61

How do I store Strings in an array?

I'm fairly new to C and I designed a simple experiment to help me understand basic I/O.

I'm creating a program that will read data from a basic .txt file, store it, and allow me to manipulate it.

In this case, I'm using MyAnimals.txt which contains:

4 Dogs
3 Cats
7 Ducks

Here is my code:

 #include <stdio.h>
 #include <stdlib.h>

 main()
 {
    char szInputBuffer[50]; //Buffer to place data in 
    FILE *pfile;

    int i;
    char szAnimalName[20]; //Buffer to store the animal name string
    char *pszAnimalNames[3]; //An array of 4 pointers to point to the animal name strings
    int  iAmountOfAnimal[3]; //An array to store the amount of each animal


    pfile = fopen("MyAnimals.txt", "r");
    printf("According to MyAnimals.txt, there are:\n");

    for (i = 0; i <= 2; i++)
    {
        fgets(szInputBuffer, 50, pfile);
        sscanf(szInputBuffer, "%d %s", &iAmountOfAnimal[i], szAnimalName);
        pszAnimalNames[i] = szAnimalName;
        printf("%d %s\n", iAmountOfAnimal[i], pszAnimalNames[i]);
    }

    printf("The number of %s and %s is %d\n", pszAnimalNames[1], pszAnimalNames[2], iAmountOfAnimal[1] + iAmountOfAnimal[2]);
    printf("The number of %s and %s is %d\n", pszAnimalNames[0], pszAnimalNames[1], iAmountOfAnimal[0] + iAmountOfAnimal[1]);
}

However my output is:

According to MyAnimals.txt, there are:
4 Dogs
3 Cats
7 Ducks
The number of Ducks and Ducks is 10
The number of Ducks and Ducks is 7

Why is it that the value pszAnimalNames[0, 1, and 2] points to "Ducks" by the end of the program?

Desired output is:

According to MyAnimals.txt, there are:
4 Dogs
3 Cats
7 Ducks
The number of Cats and Ducks is 10
The number of Dogs and Cats is 7

Upvotes: 1

Views: 68

Answers (1)

amo
amo

Reputation: 4340

char *pszAnimalNames[3];

does not allocate any memory for the text. So every time you assign something to it, you are actually pointing to szAnimalName, which is 'Ducks' at the end of the program.

This line:

pszAnimalNames[i] = szAnimalName;

actually says that pszAnimalNames[i] should take the value that szAnimalName points to. So at the end of the loop, every value in pszAnimalNames points to the same location. Even though you are changing the contents of szAnimalName, its location remains the same.

that line should instead say

pszAnimalNames[i] = (char *)malloc(sizeof(char)*20);
memcpy(pszAnimalNames[i], szAnimalName, 20);

That will allocate space for the string and copy it to the list of names. Then at the end of your program, you will need to free the memory:

for (i = 0; i <= 2; i++) {
    free(pszAnimalNames[i]);
}

Upvotes: 1

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