Populating values to a pointer array

Question

Off lately I have taken up the task to understand and learn C. Right now I was learning about structures and pointer arrays. I have a problem. I want to populate a pointer array with values. Below is my code:

           struct profile_t 
          {
           unsigned char length;
           unsigned char type;
           unsigned char *data;
          };

          typedef struct profile_datagram_t
         {
          unsigned char src[4];
          unsigned char dst[4];
          unsigned char ver;
          unsigned char n;
          struct profile_t profiles[MAXPROFILES];       
         } header;

          header outObj;

         int j =0;
         int i =0;

      outObj.profiles[j].data = malloc(10);

      for(i=0;i<10;i++)
          {
         if (j=0)
             {
           outObj.profiles[j][i] = 1 2 3 4 5 6 7 8 9 10;
         }
         else 
             {
        j=1;
         }
      }

      for(i=0;i<10;i++)
          {
        if (j=1)
            {
           outObj.profiles[j][i] = 1 2 3 4 5 6 7 8 9 10;
        }
      }

Is the above approach the way to go or am I completely offtrack. MAXPROFILES is 2 (which means only 0 and 1).

"MAXPROFILES is just 1 (which means only 0 and 1)": no, it means only 0: outObj.profiles[0] is valid; outObj.profiles[1] is not valid. — pmg
– pmg, Commented Jul 27, 2011 at 21:04
@pmg: thanks, so if MAXPROFILES is 2, then outObj.profiles[1] is valid. And the way I am initialzing the element...is that the proper way to go?? — user537670
– user537670, Commented Jul 27, 2011 at 21:07
No, you can't do it that way. You'll have to use another loop. — Rudy Velthuis
– Rudy Velthuis, Commented Jul 27, 2011 at 21:11
@anon: I do not think so, at least I have never ever seen this kind of initializer... see my code snippet! — Mario The Spoon
– Mario The Spoon, Commented Jul 27, 2011 at 21:11

eugene_che · Accepted Answer · 2011-07-27 21:23:17Z

1

You cannot assign like this

outObj.profiles[j][i] = 1 2 3 4 5 6 7 8 9 10;

outObj.profiles[j] is profile_t instance. outObj.profiles[j].data is char*. I suppose that you want to assign that integers to data. First of all you should allocate memory for both j values.

outObj.profiles[0].data = malloc(10);
outObj.profiles[1].data = malloc(10);

I suggest you to replace your code with loops with something like this

for(i=0;i<10;i++) {
    outObj.profiles[0].data[i] = i+1;
    outObj.profiles[1].data[i] = i+1;
}

The result is same but it is much cleaner to read and understand.

edited Jul 27, 2011 at 21:23

answered Jul 27, 2011 at 21:10

eugene_che

1,99712 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Rudy Velthuis Over a year ago

Was the repetition of the lines in the last code piece a copy and paste error or did you mean to use 0 and 1 respectively, instead of 'j`?

eugene_che Over a year ago

@Rudy it was old copy-paste ;-) Fixed it.

eugene_che Over a year ago

@user it depends on the way you get these numbers. If they are stored anywhere you should copy them one-by-one. If you are getting them as a result of some function you should call it inside of the cycle and generate numbers one-by-one either....

user537670 Over a year ago

@tyz: Thanks for pointing me in the right direction, but as a curious learner of "C", suppose instead of 2 MAXPROFILES, i had 50, don't you think it is cumbersome to write outOBJ.profiles[0], then [1]...[50]...won't a loop be beneficial???

eugene_che Over a year ago

@user Yes, if there are a lot of objects loop is a necessity.

Mario The Spoon · Accepted Answer · 2011-07-27 21:09:59Z

0

Or in short:

#define DATALENGTH 10

uint actProfile = 0;
uint actData = 0;



for( actProfile = 0; actProfile < MAXPROFILES; ++actProfile )
{
    outObj.profiles[actProfile].data = malloc(DATALENGTH);

    //skip check if malloc was successfull...

    for ( actData = 0; actData < DATALENGTH; ++actData )
    {
      outObj.profiles[actProfile].data[actData] = actData +1;
    }
}

answered Jul 27, 2011 at 21:09

Mario The Spoon

4,8591 gold badge28 silver badges36 bronze badges

1 Comment

user537670 Over a year ago

:If the data can be anything...not necessarily 1,2,3,4,.....then my code should work right??

pmg · Accepted Answer · 2011-07-27 21:12:16Z

0

You don't allocate space for outObj.profiles[1].data.

The sequence of numbers (1 2 ... 10) is a syntax error. You may want to use the loop variable

for (i = 0; i < 10; i++) {
    outObj.profiles[0][i] = i + 1;
}

answered Jul 27, 2011 at 21:12

pmg

109k14 gold badges132 silver badges203 bronze badges

Collectives™ on Stack Overflow

Populating values to a pointer array

3 Answers 3

5 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related