How do I dynamically create an array of strings using scanf in C

Question

So I have been searching through stack overflow for a little over an hour and I don't understand why this function is giving me a segmentation error. I want to create a string array, scan strings in through scanf, dynamically change the size of each string and return the string array. Can anyone help? Thank you.

char** readScores(int* count) {
    int c = 0;
    char** arr =(char**)malloc(100 * sizeof(char*));
    char* in;
    while(scanf("%s", in) != EOF) {
        arr[c] = (char*)malloc(strlen(in)+1);
        strcpy(arr[c], in);
    }
    *count = c;
    return arr;
}

Did you read your book? Consult and study the documentation for the features you've used? Step through the program with your debugger? Just searching SO for an hour isn't going to cut it as far as debugging goes. — Asteroids With Wings
– Asteroids With Wings, Commented Oct 5, 2020 at 22:53
I would do this but my professor didn't provide us a book and I am using emacs on a linux system without a debugger. — kylejw
– kylejw, Commented Oct 5, 2020 at 22:54
Then you need to get a book, and you need to install a debugger. — Asteroids With Wings
– Asteroids With Wings, Commented Oct 5, 2020 at 22:54

Asteroids With Wings · Accepted Answer · 2020-10-05 22:54:30Z

1

char* in;
while(scanf("%s", in) != EOF) {

This tells the computer to read from standard input into the char buffer that in points to.

Which does not exist, because in is not initialised to anything (let alone a valid buffer).

answered Oct 5, 2020 at 22:54

Asteroids With Wings

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0___________ · Accepted Answer · 2020-10-05 23:34:01Z

I would not use scanf only fgets.

You need to allocate memory dor the arr and for every line referenced by elements of arr

char** readScores(size_t *count) {
    size_t lines = 0;
    char** arr = NULL, **tmp;
    char* in = malloc(MAXLINE), *result;
    size_t len;

    if(in)
    {
        do{
            result = fgets(in, MAXLINE, stdin);           
            if(result)
            {
                len = strlen(in);
                tmp = realloc(arr, sizeof(*tmp) * (lines + 1));
                if(tmp)
                {
                    arr = tmp;
                    len = strlen(in);
                    arr[lines] = malloc(len + (len == 0));
                    if(arr[lines])
                    {
                        if(len) memcpy(arr[lines], in, len - 1);
                        arr[lines++][len] = 0;
                    }
                    else
                    {
                        // error handling     
                    }
                }
                else
                {
                    // error handling 
                }
            }
        }while(result);
        free(in);
    }
    *count = lines;
    return arr;
}

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