CODEWITHSUNDEEP
carraysdynamicchar
QWERTY
QWERTY

Reputation: 2315

Insert element into dynamic char array in C programming

I was having some problem when trying to add element to dynamic char array in C programming. Here is the expected output:

How many characters do you want to input: 5
Input the string:datas
The string is: datas
Do you want to 1-insert or 2-remove or 3-quit?: 1
What is the character you want to insert: a
Resulting string: adata

I already did those user input part in the main function and here is the code in main where I take in the string input, size and pass them to insert():

printf("How many characters do you want to input: ");
scanf("%d", &n);
str = malloc(n + 1);
printf("Input the string class: ");
scanf("%s", str);

case '1':
    printf("What is the character you want to insert: ");
    scanf(" %c", &input);
    insert(str, input, n);
    break;

And the part where my insert():

void insert(char *str, char input, int n) {
int i;
size_t space = 1;
for (i = 0; i < n; i++) {
    str[i] = (char)(input + i);
    space++;                       
    str = realloc(str, space); 
    if (i > 2) {
        break;
    }
}

for (i = 0; i < n; i++) {
    printf("%c", str[i]);
}
}

However, when I tried to print out the string from insert(), let's say I entered 'a' to append to the first element of dynamic array with a size of 5, the result that I am getting is abcd=

I referenced from the stackoverflow thread and I not sure how to fix this. Thanks in advance.

Upvotes: 0

Views: 6658

Answers (2)

Ed Heal
Ed Heal

Reputation: 60007

Here is the code - with the contract that the caller does the free bit! The caller calls it with insert(&str, input, n)

void insert(char **str, char input, int n) {

char* temp = *str;
int i;

*str = realloc(*str, n + 2); /* realloc first */

if(!*str) /* realloc failed */
{
    fputs("realloc failed", stderr);
    free(temp); /* Free the previously malloc-ed memory */
    exit(-1); /* Exit the program */
}

for (i = n; i >= 0; i--) {
    (*str)[i + 1] = (*str)[i]; /* Move all characters up */ 
}

(*str)[0] = input; /* Insert the new character */

printf("%s", *str); /* Print the new string */
}

Sorry about the formatting. That is left to the reader. I have not checked the algorithm but this does not leak memory

Upvotes: 1

Spikatrix
Spikatrix

Reputation: 20244

You can use

void insert(char **str, char input, int n) {

    char* temp = *str;
    int i;

    *str = realloc(*str, n + 2); /* realloc first */

    if(!(*str)) /* realloc failed */
    {
        fputs("realloc failed", stderr);
        free(temp); /* Free the previously malloc-ed memory */
        exit(-1); /* Exit the program */
    }

    for (i = n; i >= 0; i--) {
        (*str)[i + 1] = (*str)[i]; /* Move all characters up */ 
    }

    **str = input; /* Insert the new character */

    printf("%s", *str); /* Print the new string */
}

And pass str by reference using

insert(&str, input, n); /* Note the '&' */

Upvotes: 1

Related Questions