Reading big numbers such as e and pi from files to arrays in C

Question

I have a file called pi.txt which contains, as you probably imagine, the numbers of pi.

The format goes like this

Line 1: 3. Line 2: 14159265358979323846264338327950288419716939937510 Line 3: 58209749445923078164062862089986280348253421170679

and it continues to

Line 20001: 56787961303311646283996346460422090106105779458151

There are 1020001 digits minus the 3 and the .(of 3.14xxxxxx...)

I have to read this file to an array (not a 2D one. What I want to do later will become much harder if I use a 2D array as I imagine it). This is my code:

void fpi();
char **arraypi;

int main(int argc, char *argv[]) {
    fpi();
    int i;
    while (i<=10){
    printf("%d", arraypi[i++]);}
    return 0;
}


void fpi(){
    char pi[1020001];
    arraypi = malloc(1020001 * sizeof(int));
    FILE *file;
    int i=0;
    file = fopen("pi.txt", "r");
    if (file == NULL){
        printf("The file cannot be opened.\n");
        exit(1);
    }
    while (fscanf(file, "%c", &pi)==1){
            strcpy(arraypi[i++], pi);
    }
    fclose(file);
}

I get a segmentation fault and I can't figure out why. I'm sure it has to do with the pointers I'm using and fscanf.

Answer 1

strcpy expects you to give a null terminated character array (string) and you're giving an array of 1020001 characters where except the first character, which is read from the file, everything else is undetermined.

char pi[1020001];
while (fscanf(file, "%c", &pi)==1){   // only one character gets copied to pi
        strcpy(arraypi[i++], pi);     // strcpy will expect pi to be a string and not just a char
}

Hence it may go on an infinite loop and write beyond the allowed memory allocated for it, thereby corrupting the stack structure and thus leading to the segmentation fault. You're also treading on undefined behaviour when you're doing this.