malloc

[Horst Kraemer]

i am having a pointer testptr to a structure test

struct
{
int a;
char b[10];
}test;

test *testptr;

This is illegal sytax. You may use

struct test
{
int a;
char b[10];
};

struct test *testptr;

or

typedef
struct
{
int a;
char b[10];
}test;

test *testptr;

or

typedef
struct anything
{
int a;
char b[10];
}test;

test *testptr;

I am doing malloc for the pointer to have memory for an array of 3
structures like below:
testptr=(testptr)malloc(sizeof(test)*3);

Again illegal syntax.

testptr=(test*)malloc(sizeof(test)*3);

would be legal but the cast (test*) isn't necessary in C.

Now how can i get to know that testptr is allocated memory for an
array of 3 strcture from the testptr variable?

testptr=malloc(sizeof *testptr *3);
if (testptr==0) { /* couldn't allocate memory */ }
or
if (testptr==NULL) { /* couldn't allocate memory */ }
or
if (!testptr) { /* couldn't allocate memory */ }

Which form you use is a matter of style. malloc returns a null pointer
if the requested memory size couldn't be allocated.

Regards
Horst

 

[harish]

i am having a pointer testptr to a structure test

struct
{
int a;
char b[10];
}test;

test *testptr;


I am doing malloc for the pointer to have memory for an array of 3
structures like below:
testptr=(testptr)malloc(sizeof(test)*3);

Now how can i get to know that testptr is allocated memory for an
array of 3 strcture from the testptr variable?

 

[user]

i am having a pointer testptr to a structure test

struct
{
int a;
char b[10];
}test;

test is a variable and hence the below line will fail. You can use the below
code.
struct test
{
int a;
char b[10];
};

struct test *testptr;

test *testptr;

this is wrong

I am doing malloc for the pointer to have memory for an array of 3
structures like below:
testptr=(testptr)malloc(sizeof(test)*3);

testptr = malloc (sizeof *testptr *3);

Now how can i get to know that testptr is allocated memory for an
array of 3 strcture from the testptr variable?

by checking the value of testptr. If it is non null then u have got what u
requested for

HTH