Dynamic Array of Structs Problem

[viperdriver87]

Greetings all, I had another post on here about a Dynamic array of ints problem, and with your help, I managed to solve that problem. Now, I've another issue. I need to dyanically allocate an array of structs.

The struct is defined as:

struct song{
 
  char name[50];
  char title[50];
 
};

So, for work, they want me to sort through the songs, but due to memory constraints on the tiny machine they want it to run on, I have to use arrays instead of Linked Lists. :( I tried this method, the way it worked with ints:

int * list;
 
list = (int *)malloc(sizeof(int) * length);

And that would actually give me an array of ints. But if I try that with the song struct, it just gives me one.

Thanks in Advance.

[ravenspoint]

Please post code that fails, i.e. the attempt to allocate an array of structs.

[RedSon]

Greetings all, I had another post on here about a Dynamic array of ints problem, and with your help, I managed to solve that problem. Now, I've another issue. I need to dyanically allocate an array of structs.

The struct is defined as:

struct song{
 
  char name[50];
  char title[50];
 
};

So, for work, they want me to sort through the songs, but due to memory constraints on the tiny machine they want it to run on, I have to use arrays instead of Linked Lists. :( I tried this method, the way it worked with ints:

int * list;
 
list = (int *)malloc(sizeof(int) * length);

And that would actually give me an array of ints. But if I try that with the song struct, it just gives me one.

Thanks in Advance.

First, using a linked list is more memory efficient then using an array. Every time you need to add to the array you will have to create an array that is one element larger and copy your existing array into the new array then delete your previous array. When this occurs you will then have a array of length N and an array of length N+1 which means that you are using virtually double the memory.

If you use a linked list, anytime you add something all you need to do is create the element then iterate to the last element in the list and reset the pointer to your new element.

The problem you may be experiencing is that the sizeof call may not work for your struct. I am not too clear on how it works exactly since I have never used it in this way. Consider trying to create your list using the sizeof (char[50]) to see if that will allocate properly, then moving on from there.

[ravenspoint]

This works:

 
      struct song{
        char name[50];
        char title[50];
 
      };
 
     int length = 10;
     song * list = (song *)malloc(sizeof(song) * length);
 
     char buf[20];
     for( int k=0; k < 10; k++ ) {
         sprintf(buf,"song #%d", k );
         strcpy( list[ k ].name, buf );
     }
 
     for( int k=0; k < 10; k++ ) {
        printf( "%s\n",     list[ k ].name );
     }
 

[mac11]

no need for me to post

[viperdriver87]

Excellent, this worked! Thanks to ravenspoint, RedSon, and mac111!