Question

I need to write a program which gets 4 arguments, the first one a string represents a binary file divided to bytes, and the second, third, and fourth (x,y,z) are 3 integers where their sum is 8. each byte has x left bits, y bits after them, and finally z bits. each group represent a number.

I need to print these numbers. For example for x=4, y=3, z=1 and file has 3 bytes:

1010 0001 1 0101 011 1 0010 001 1 the result would be 10 0 1 5 3 1 2 1 1.

I’d like your help with files in C. This is what I wrote:

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

#define  SEEK_SET   0

#define  SEEK_CUR   1

#define  SEEK_END   2

int main(int argc, char** argv) {

    if (argc!=5) {
        printf("enter a file name and 3 integers such that their sum is 8");
        return 0;
    } else {
        FILE* f;
        f=fopen(argv[1], "r");
        if (f==NULL) {
            printf("File %s does not exists \n", argv[1]);
            return 0;
        }

        else {
            int length=0;
            int offset=0;
            fseek(f, 0, SEEK_END);
            length=ftell(f);
            fseek(f, 0, SEEK_SET);

            while (offset < length) {
                int i;
                double sum=0;
                for (i=1; i<= atoi(argv[2]); ++i) {
                    double exponent= atoi(argv[1])- i;
                    sum=getc(f)*pow(2, exponent); 

                }
                printf("%d ", (int)sum);
                sum=0;

                for (i=1; i<= atoi(argv[3]); ++i) {
                    double exponent= atoi(argv[1])- i;
                    sum=fetc(f)*pow(2, exponent);
                }
                printf("%d ", (int)sum);
                sum=0;
                for (i=1; i<= atoi(argv[4]); ++i) {
                    double exponent= atoi(argv[1])- i;
                    sum=getc(f)*pow(2, exponent);
                }
                printf("%d ", (int)sum);
                offset+=8;
            }
            fclose(f);
        }

    }
    return 0;
}

Couple of questions:

1. I copy the whole argc, **argv from other program which use files. is this Ok? I mean when I enter main c:\stackExchange 5 2 1 would it automatically give 4 to argc and an array of the other parameters as strings? I assumed it does, and wrote the above.
2. I assumed that getc(f) returns a bit, is this correct?

any other corrections would be gladly welcome.

Answer 1

Regarding your first question, argc is the number of entries in the argv array, i.e. the number of arguments plus one. So for your example command line argc would be 5, with argv containing this:

argv[0] : "main"
argv[1] : "c:\\stackExchange"
argv[2] : "5"
argv[3] : "2"
argv[4] : "1"
argv[5] : NULL

Regarding your second question, getc returns an integer, which if it’s not EOF can be interpreted as a character or a byte depending on if you read text or binary data.