malloc struct

[palidhjede]

Hi I'm having difficulties trying to malloc a struct this is what it looks like and how I'm approaching the problem.

struct Records
{
  char * fname;
  char * lname;
};

Records**   g_Recs; //Array of pointers


void fakefunc()
{
 g_Recs = (struct StudentRecords **) malloc (sizeof(struct StudentRecord*));
 g_Recs = (struct Records *) malloc (sizeof(struct StudentRecord));

 g_Recs->fname= (char *) malloc(strlen(buffer));


}

Thats a very basic example of my code. I get an error that ->fname must point to class/struct/union/generic type.

I'm assuming that I am not mallocing the struct properly and thats is why im getting this erro. If anyone could help me with this, I would greatly appreciate it.

[weaknessforcats]

struct Records
{
char * fname;
char * lname;
};

Records**   g_Recs; //Array of pointers

This is not an array of pointers. This is one pointer that is a pointer to a Record.

Remember, the name of the array is the address of element 0. Therefore, if g_Recs is an array of Records, then g_recs is the address of element 0. That makes g_recs the address of a Records.

That is, g_recs is a Records*.

To allocate an array of records you need to know how many Records are in the array. Let's say there are 20. So you allocate memory for 20 Records:

Records* g_recs = malloc(sizeof(Records) * 20);

[palidhjede]

Thank you for the clarification, but I'm still unsure of the meaning of the double star **. As well I'm not sure how i would malloc one of the members of the struct. If you or someone could show me an example of mallocing a struct that is declared the way mine is (with the **) I would greatly appreciate it. Thanks for your time

[donbock]

struct Records {
    char *fname;
    char *lname;
};

// Relationship between object, pointer, and pointer-to-pointer.
struct Records theRecord;
struct Records *pRecord = &theRecord;
struct Records **ppRecord = &pRecord;

// How to access a record.
char *pText;
pText = theRecord.fname;
pText = pRecord->fname;
pText = (*ppRecord)->fname;   // I'm not sure about this one.

Suppose sizeof(void*) on this platform is 4. Then sizeof(theRecor d) is 8, sizeof(pRecord) is 4, and sizeof(ppRecord ) is 4.

I don't know if the parentheses are needed in the last pText example.

In general to avoid confusion, you should have a very good reason for using double-start pointers-to-pointer. As a rule, you should never use triple-star pointers-to-pointer-to-pointer or beyond. There are exceptions but they don't arise often.

What are you trying to do that led you to believe that a double-star pointer would be helpful?