What am I doing wrong with malloc and realloc of array of struct?

I'm trying to build in C an array of structures without defining the length of the maximum size of the array.

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

typedef struct text {
   char *final;
} text;

int main() {
    int n, sizearray = 10, i;
    char *str;
    text *testo;
    testo = (text *)malloc(sizeof(text) * sizearray);

    fgets(str, 1024, stdin);
    i = 0;
    while (str[0] != 'q') {
        if (i == sizearray - 1) {
            testo = (text *)realloc(testo, sizearray * 2 * sizeof(text));
        }
        n = strlen(str);
        n = n + 1;
        testo[i].finale = (char *)malloc(sizeof(char) * n);
        strcpy(testo[i].finale, str);
        i++;
        fgets(str, 1024, stdin);
    }

    for (i = 0; i < sizearray; i++)
        printf("%s \n", testo[i].finale);

    return 0;
}

this gives me

process finished with exit code 139 (interrupted by signal 11:SIGSEV).

What am I doing wrong?

Solution

There are multiple issues in your code:

[major] str is an uninitialized pointer. You should make it an array of char defined with char str[1024].
[major] you do not adjust sizearray when you double the size of the array, hence you will never reallocate the array after the initial attempt at i = 9.
[major] the final loop goes to sizearray but there are potentially many uninitialized entries at the end of the array. You should stop at the last entry stored into the array.
you should also check the return value of fgets() to avoid an infinite loop upon premature end of file.
you should test for potential memory allocation failures to avoid undefined behavior.

Here is a modified version:

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

typedef struct text {
   char *finale;
} text;

int main() {
    char str[1024];
    text *testo = NULL;
    size_t sizearray = 0;
    size_t i, n = 0;

    while (fgets(str, sizeof str, stdin) && *str != 'q') {
        if (n == sizearray) {
            /* increase the size of the array by the golden ratio */
            sizearray += sizearray / 2 + sizearray / 8 + 10;
            testo = realloc(testo, sizearray * sizeof(text));
            if (testo == NULL) {
                fprintf(stderr, "out of memory\n");
                return 1;
            }
        }
        testo[n].finale = strdup(str);
        if (testo[n].finale == NULL) {
            fprintf(stderr, "out of memory\n");
            return 1;
        }
        n++;
    }

    for (i = 0; i < n; i++) {
        printf("%s", testo[i].finale);
    }
    for (i = 0; i < n; i++) {
        free(testo[i].finale);
    }
    free(testo);
    return 0;
}