Thread: array of pointers of a struct

I've got an array of struct pointers as following

Code:

struct record{....}
struct record*[]

and two methods:

Code:

create_a_record(struct record*)
create_record_array(struct record*[])

Basically, create_a_record() is to create an individual record, while create_record_array() is to create an array by calling create_a_record() in a loop.

My question is here:
if the memory for an individual record pointer is declared in the loop of create_record_array(), it's fine; if it's declared in create_a_record(), then it fails. the code is like the following:

Code:

int create_record_array(struct record* recs[], int rec_no){
      int i;
      for ( i = 0; i < rec_no; i++ ){
            //if declare here, work!
            recs[i] = malloc( sizeof( struct record) );
            create_a_record( recs[i] );
      }

      return i;
}

struct record* create_a_record(struct record* rec){
      //if declared here, does NOT work!
      rec = malloc( sizeof( struct record) );
      ......

}

Many thanks!

Paul

Sorry about the confusing code.

What i want to ask is that if

Code:

recs[i] = malloc( sizeof( struct record) );

is declared in create_record_array(), the program runs correctly; but if the code is put in create_a_record(), it doesn't.

Many thanks!

Paul

Salem,

Thanks for reply.

The problem is that if malloc() is put in the loop of create_rec_array(), the program works; but if malloc() is in create_an_rec(), it does not work. That's my question.

Sorry for the mispresentation.

Paul

Here is the code:

Code:

struct record * build_record(struct record* rec, int rec_id){
        //comment 1   ????
        //rec   = (struct record *)malloc(sizeof( struct record));
        rec->id         = rec_id;

        return rec;
}

int build_records(struct record* records[]){
        int i;
        for ( i = 0; lines[i] < 5; i++ ){
                //comment 2
                records[i] = (struct record *)malloc(sizeof( struct record));
                build_record( records [i], i );
         }

        return i;
}

My question is that if malloc(sizeof( struct record)) is used at //comment 2, the program works; if malloc(sizeof( struct record)) is used at //comment 1, the program does not work.

Many thanks!

Paul

looking at your code it seems that it won't work. in create_an record fucntion u call malloc fucntion and allocate space for an record. when u leave that f........ion it's left there. what u where suppose to do is to return the allocated record back to the fucntion create_an_array as show bellow

Code:

struct Record *create_an_array(struct Record *recs[], int rec_no)
{
    int i;
    
    for(i=0;i<10;i++)
        recs[i] = create_an_record(recs[i]);
}

struct Record *create_an_record(struct Record *rec)
{
    rec = malloc(sizeof(struct Record));
    rec->data =10;   // some data filling code
    rec->ch='c';

    return rec;
}

//---- > my struct skeleton < ------
struct Record
{
    int data;
    char ch;
};

/*my output
10  c
10  c
10  c
10  c
10  c
10  c
10  c
10  c
10  c
10  c
*/

ssharish2005

ssharish2005,

Thanks for the message.

My real code is a bit more than what is shown, but like following:

Code:

struct record * build_record(struct record* rec, int rec_id){
        string words[] = {"hello", "world"};
        //comment 1 ????
        //rec   = (struct record *)malloc(sizeof( struct record));
        rec->id         = rec_id;
        rec->name       = words[0];
        rec->remark     = words[1];

        return rec;
}

It doesn't seem to work if malloc() is used at comment 1.....


Paul

it should work if u do it like that. i guess u'r problem is with the create_an_array fucntion. u are not getting the record which is returned by the create_an_record fucntion.

Code:

int i;
        for ( i = 0; lines[i] < 5; i++ ){
                //comment 2
                //records[i] = (struct record *)malloc(sizeof( struct record));
                records[i] = build_record( records [i], i );
         }

        return i;

ssharish2005

it shouldn't be like that

post your whole code let's have look at it

ssharish2005

ssharish2005,

Here is the code. You can see at line 18, which is commented because malloc() doesn't work here, and i've got to put it at line 35.

Code:

    14 struct record * build_record(struct record* rec, int rec_id, string line, string sep){
     15         string words[MAX_FIELD];
     16         parse_line(words, line, sep);
     17
     18         //rec   = (struct record *)malloc(sizeof( struct record));
     19         rec->id         = rec_id;
     20         rec->name       = words[0];
     21         rec->birth[0]   = 1;
     22         rec->birth[1]   = 2;
     23         rec->birth[2]   = 3;
     24         rec->remark     = words[2];
     25         rec->status     = '1';
     26
     27         printf("build record:\t");
     28         display_record( rec );
     29         return rec;
     30 }
     31
     32 int build_records(struct record* records[], string lines[], string sep){
     33         int i;
     34         for ( i = 0; lines[i] != NULL; i++ ){
     35                 records[i] = (struct record *)malloc(sizeof( struct record));
     36                 build_record( records [i], i, lines[i], sep );
     37
     38                 printf("check record after built, ");
     39
     40                 printf("Record: id: %d, dob: %d, name: %s, remark: %s\n",
     41                         records[i]->id, records[i]->birth[0], records[i]->name, records[i]->remark);
     42
     43         }
     44
     45         return i;
     46 }