How can I allocate memory for structure pointer

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i have two structure

C

struct list
{
	char *name;
	int ID;
	int marks[5];
}

struct Employee
{  
    char *school_name;
    unsigned long int ID;
    struct list * student_list;  
	//here i want to use pointer only, because i don't know student si
};

struct Employee high_list;

Here i want to 20 students name, ID, marks for one school; like

C

high_list.student_list[0].ID =20;
high_list.student_list[2].ID =20;
high_list.student_list[3].ID =30;
high_list.student_list[4].ID =30;
high_list.student_list[0].mark[0] =20;
high_list.student_list[2].mark[1] =20;
high_list.student_list[3].mark[0] =30;
high_list.student_list[4].mark[4] =30;

How can i do memory allocation for 20 student list;
.student_list=(struct list *)malloc(sizeof(struct list)); //this is for one list
if i do(struct list) *20 ???

want to allocate for 20 students

What I have tried:

dynamic memory alocation
malloc(sizeof(struct list)*20)

Posted 19-Nov-22 0:59am

jagan18_

Updated 19-Nov-22 8:53am

merano99

v2

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CPallini · Answer 1 · 2022-11-19T01:10:00

Indeed you may either use

C

high_list.student_list = (struct list *) malloc( sizeof(struct list ) * 20);

or

C

high_list.student_list = (struct list *) calloc( 20, sizeof(struct list) );

By the way, remember to:

Check the return value of the malloc (or calloc) call, since memory allocation might fail.
Free the allocated memory when you don't need it any longer.

merano99 · Answer 2 · 2022-11-19T02:51:00

Palini's solution works as proposed.

C

struct Employee high_list;

high_list.student_list = (struct list *) calloc(20, sizeof(struct list));
if (high_list.student_list == NULL) return -1;

Of course, the includes <stdio.h> and <stdlib.h> must be used and there should be a semicolon at the end of a structure definition.

Attention: For the strings name and school_name you also need memory as soon as you use them!

Rick York · Answer 3 · 2022-11-19T08:53:00

Solution 4

I use a macro for this :

C++

#define AllocateMemory(count,type)	(type*)calloc(count,sizeof(type))

   // and how it's used

   high_list.student_list = AllocateMemory( 20, struct list );

Posted 19-Nov-22 8:53am

Rick York

Updated 19-Nov-22 8:54am

v2

How can I allocate memory for structure pointer

3 solutions

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