Pointer in C

A simple example to using pointer in C.

we claim a pointer in main function, and hope to pass it to subroutin to allocate the memory.

How to use it?

Solution 1, return the address back.

=======================

#include

#include

int array_size =10;

int fill_array( float *ptr)

 {

    int i;

printf("Address %d\n", &ptr);

    ptr = (float *) malloc(array_size *sizeof(float));

    for(i=0; i<>

    {

         

      ptr[i] = (float)i;

    }

    

   for(i=0; i

   {

 printf("In function\n");

 

      printf("%d - %f ", &ptr[i],ptr[i]);

   }

   printf("\n");

   printf("ptr = %d\n", &ptr);

   return(ptr);

 }

main()

{

float *ptr = NULL;

int i;

printf("Address %d\n", &ptr);

ptr=fill_array(&ptr);

printf("Out function\n");

printf("Address %d\n", &ptr);

for(i=0; i

{

printf("Out function\n");

printf("%d - %f ", &ptr[i], ptr[i]);

}

}

=======================

The result will be

-------------------------------------

Address 1245052 //ptr in main( )

Address 1244968 //ptr in fill_array( )

In function

4397824 - 0.000000 In function

4397828 - 1.000000 In function

4397832 - 2.000000 In function

4397836 - 3.000000 In function

4397840 - 4.000000 In function

4397844 - 5.000000 In function

4397848 - 6.000000 In function

4397852 - 7.000000 In function

4397856 - 8.000000 In function

4397860 - 9.000000

ptr = 1244968  //ptr in fill_array( )

Out function

Address 1245052

Out function

4397824 - 0.000000 Out function

4397828 - 1.000000 Out function

4397832 - 2.000000 Out function

4397836 - 3.000000 Out function

4397840 - 4.000000 Out function

4397844 - 5.000000 Out function

4397848 - 6.000000 Out function

4397852 - 7.000000 Out function

4397856 - 8.000000 Out function

4397860 - 9.000000 Press any key to continue

-------------------------------------

Solution 2 , call by address.

=======================

#include

#include

void function(float ** ptrf)

{

int i;

printf("address of *ptrf = %d\n", &*ptrf);

*ptrf = (float *) malloc(5*sizeof(float*));

printf("address of *ptrf = %d\n", &*ptrf);

for(i=0; i<5;>

{

(*ptrf)[i] =i;

}

}

int main()

{

float *ptr=NULL;

int i;

printf("address of *ptr = %d\n", &ptr);

function(&ptr);

for(i=0; i<5;>

{

printf("%f ", ptr[i]);

}

printf("\nAddress ponited to by the ptr out function \nptr=%d, &ptr=%d\n", ptr, &ptr);

}

=======================

The result will be

---------------------------------

address of *ptr = 1245052

address of *ptrf = 1245052

address of *ptrf = 1245052

0.000000 1.000000 2.000000 3.000000 4.000000

Address ponited to by the ptr out function

ptr=4397856, &ptr=1245052

Press any key to continue

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