Question

Right now, I have

int main(int argc, char *argv[]) {
    if (argc != 3) {
        printf("Invalid number of command line parameters, exiting...\n");
        exit(1);
    }

    int *numReadings;
    load_readings(argv[1], numReadings);

    return 0;
}

    int *load_readings(char fileName[], int *numReadings) {
        FILE *in = NULL;
        in = fopen(fileName, "r");

        if (in == NULL) {
            printf("Unable to open a file named \"%s\", exiting...\n", fileName);
            fclose(in);
            exit(4);
        }

        printf("%s\n", fileName);
        int size = atoi(fileName);
        printf("Size is %d\n", size);
        int *data = (int *) calloc(size, sizeof(int));

        int i;
        for (i = 0; i < size; i++)
            fscanf(in, "%d", (data + i));
        }
    }

And When I do size = atoi(fileName) it returns 0. On multiple sites including this one, I’ve seen people do “atoi(argv[1])” but mine constantly returns 0. My sample.txt file has a bunch of 3-digit numbers separated by spaces. I am under the impression that once I get the size correctly, everything else below it will work.

Answer 1

atoi does not tells size, it just converts string into integer.
for knowing size of file you need to seek to the end of the file and then ask for the position:

    fseek(fp, 0L, SEEK_END); // seek to end of file
    size = ftell(fp);    //get current file pointer
   fseek(f, 0, SEEK_SET); // seek back to beginning of file