Typedef struct questions

Projects Programming
37

consider code below, run on laptop with following output

it first displays the "empty" array. then adds two entries with "keys" "a" and "b". then processes two additional entries with keys "a" and "c", the one with key "a" overwriting the existing entry for "a"

dispMyDataSet:
 0:
 1:
 2:
 3:
 4:

dispMyDataSet:
 0: a  AB  UQ  -129  AB
 1: b  NB  OU  -123  JB
 2:
 3:
 4:

dispMyDataSet:
 0: a  OP  QX  -151  YZ
 1: b  NB  OU  -123  JB
 2: c  bb  oo  -100  jj
 3:
 4:

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

typedef struct {
  char messageFromPC [2];
  char sID[3];
  char dID[3];
  char pRssI[5];
  char route[3];
} MyDataSet_t;

#define N_DATA  5
MyDataSet_t myDatatable [N_DATA] = {};

// -----------------------------------------------------------------------------
MyDataSet_t *
searchMyDataSet (
    char *s )
{
    MyDataSet_t *p = & myDatatable [0];

    // search for matching entry
    for (unsigned i = 0; i < N_DATA; i++, p++)
        if (! strcmp (p->messageFromPC, s))
            return p;

    // search for empty entry
    p = & myDatatable [0];
    for (unsigned i = 0; i < N_DATA; i++, p++)  {
        if (! *(p->messageFromPC))
            return p;
    }
    
    return 0;
}

// -----------------------------------------------------------------------------
void
readMyDataSet (
    char *buf )
{
    char         tempChars [80];
    char        *key;

    strcpy (tempChars, buf);
    strcpy (key, strtok (tempChars, ", "));

    MyDataSet_t *p = searchMyDataSet (key);

    if (0 == p)  {
        printf ("%s: no available entry\n", __func__);
        return;
    }

    strcpy (p->messageFromPC,   key);
    strcpy (p->sID,             strtok (NULL, ", "));
    strcpy (p->dID,             strtok (NULL, ", "));
    strcpy (p->pRssI,           strtok (NULL, ", ")); 
    strcpy (p->route,           strtok (NULL, ", "));
}

// -----------------------------------------------------------------------------
void
dispMyDataSet (void)
{
    MyDataSet_t *p = myDatatable;

    printf ("%s:\n", __func__);
    for (int n = 0; n < N_DATA; n++, p++)
        printf (" %d: %s  %s  %s  %s  %s\n", n, 
            p->messageFromPC, p->sID, p->dID, p->pRssI, p->route);
    printf ("\n");
}

// -----------------------------------------------------------------------------
int
main ()
{
    dispMyDataSet ();

    readMyDataSet ("a,AB,UQ,-129,AB");
    readMyDataSet ("b,NB,OU,-123,JB");
    dispMyDataSet ();

    readMyDataSet ("a,OP,QX,-151,YZ");
    readMyDataSet ("c,bb,oo,-100,jj");
    dispMyDataSet ();

    return 0;
}