Demonstrate what lies beneath: clang & gcc

hw077.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <limits.h>

#include "../snap.h"

int main(int argc, char const * argv[]) {

  char carry[9] = { 'c', 'a', 'f', 'e', 'b', 'a', 'b', 'e', '\0', };
  size_t carry_sz = sizeof(carry);
  short sarry[2] = { SHRT_MIN, SHRT_MAX, };
  size_t sarry_sz = sizeof(sarry);

  void * cap_b = &carry;
  void * cap_e = cap_b + carry_sz;
  void * sap_b = &sarry;
  void * sap_e = sap_b + sarry_sz;
  void * sb;
  void * se;
  size_t s_sz;

  if (sap_b > cap_b) {
    sb = cap_b;
    se = sap_e;
  }
  else {
    sb = sap_b;
    se = cap_e;
  }
  s_sz = se - sb;

  printf("cap  - %p, %p, %zu\n", cap_b, cap_e, carry_sz);
  printf("sap  - %p, %p, %zu\n", sap_b, sap_e, sarry_sz);

  printf("snap - %p, %p, %zu\n", sb, se, s_sz);
  snap(stdout, sb, s_sz);

  return 0;
}

hw077.log

$ # Compiled with clang:
$ clang -Wall -std=gnu18 -o ./hw077 hw077.c ./snap.c && ./hw077 
cap  - 0x7ffedfee344f, 0x7ffedfee3458, 9
sap  - 0x7ffedfee342c, 0x7ffedfee3430, 4
snap - 0x7ffedfee342c, 0x7ffedfee3458, 44
0x7ffedfee342c:
0000: 0080ff7f09000000 000000008834eedf fe7f000000000000 0100000000000000  ........ .....4.. ........ ........ 
0020: 0000006361666562 61626500                                            ...cafeb abe.                       

$ # Compiled with GNU gcc:
$ gcc-10 -Wall -std=gnu18 -o ./hw077 hw077.c ./snap.c && ./hw077 
cap  - 0x7ffee007a40f, 0x7ffee007a418, 9
sap  - 0x7ffee007a40a, 0x7ffee007a40e, 4
snap - 0x7ffee007a40a, 0x7ffee007a418, 14
0x7ffee007a40a:
0000: 0080ff7f00636166 656261626500                                        .....caf ebabe.                     

snap.c

#include "snap.h"

//  MARK: - Implementation.
/*
 *  MARK: snap()
 *  SVC 51 (0A33)
 */
int snap(FILE * fp, void const * opvar, size_t op_l) {

  octet const * op = (octet const *) opvar;
  int chr_ct = 0;

  size_t const LL = 0x20; //  snap line length (32)
  size_t const GP = 0x08; //  distance between print gaps
  octet const * op_end = op + op_l;
  octet const * op_now = op;

  chr_ct += fprintf(fp, "%p:\n", op);
  while (op_now < op_end) {
    octet const * hex_p = op_now;
    octet const * chr_p = op_now;

    chr_ct += fprintf(fp, "%04" PRIxPTR ": ", hex_p - op);
    for (size_t xc = 0, sp = 1; xc < LL; ++xc) {
      octet const * loc = hex_p++;
      if (loc < op_end) {
        octet x_ = *loc;
        chr_ct += fprintf(fp, "%02" PRIx8 "%s", x_, (sp++ % GP == 0) ? " " : "");
      }
      else {
        chr_ct += fprintf(fp, "  %s", (sp++ % GP == 0) ? " " : "");
      }
    }
    chr_ct += fprintf(fp, " ");

    for (size_t cc = 0, sp = 1; cc < LL; ++cc) {
      octet const * loc = chr_p++;
      octet c_ = loc < op_end ? *loc : ' ';
      chr_ct += fprintf(fp, "%c%s", isprint(c_) ? c_ : '.', (sp++ % GP == 0) ? " " : "");
    }
    chr_ct += fprintf(fp, "\n");
    op_now += LL;
  }
  chr_ct += fprintf(fp, "\n");

  return chr_ct;
}

snap.h

//
//  snap.h
//  CF.snap
//
//  Created by Alan Sampson on 6/22/20.
//  Copyright © 2020 Alan @ FreeShell. All rights reserved.
//

#ifndef snap_h
#define snap_h

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdint.h>
#include <inttypes.h>
#include <ctype.h>

//  MARK: - Definitions.
typedef uint8_t octet;

int snap(FILE * fp, void const * op, size_t op_l);

#endif /* snap_h */