C string array

[galaxy_virus]

Hello,

I am newbie in C. I stored strings in array. (I know that string itself is an array. ) There is error when I compile and run the program. But I need to be sure that the following idea is correct or not since I dont want to meet unnecessary problems later.

I'd like push strings onto the stack_array using a loop or function call.

For example, it will look like:

stack[0]  =  " This is first line";
stack[1]  =  " This is second line";
.....
.....
.....
stack[i]  = " This is last line";

// global variable declaration 

const int  depth = 30;
char*  Stack[depth ];
int index= 0                    


function Add_data_to_stack (char *data, int data_length)
{

          // memory allocation for stack[index] happened here

    	 strncpy(Stack[index],data,data_length);   // copy data to stack[index]
    	 Stack[counter][len] = '\0';                        //  adding zero terminated character
      
         index++;
        
     // release memory allocation here  ( free ()  )
}

[galaxy_virus]

Hmmm.. I can't edit my post. There are some typos. I am sorry.

I wanted to mean that there is *no* error when I compile and run the program.

[C_ntua]

Why would you release memory allocation inside the Add_data_to_stack fucntion? You want to release memory allocated (with free() ) when you don't want it anymore. Make another function Destory_stack() to do this job.

Aslo, since you have the depth of the stack use it in order to avoid overflows. You can do something this at the very start of the Add_data_to_Stack.

if (index > depth-1) {
   printf("Stack full!\n");
   return;
}

[galaxy_virus]

Why would you release memory allocation inside the Add_data_to_stack fucntion? You want to release memory allocated (with free() ) when you don't want it anymore. Make another function Destory_stack() to do this job.

Aslo, since you have the depth of the stack use it in order to avoid overflows. You can do something this at the very start of the Add_data_to_Stack.

if (index > depth-1) {
   printf("Stack full!\n");
   return;
}

Hello C-ntua,

Thanks for your very prompt reply. I will check depth of the stack as per your suggestion.

For memory allocation, I have one question. Whenever function is called,
I need to allocate the memory for stack[index] ( index is somehow incremented).
So if I free memory in different function, how can I reallocate the memory here?
'though I know there is realloc(), I dont know how to control it.
Here is my naive idea.

such as.. If ( index = 1 )
malloc();

else
realloc();

[Elysia]

The idea is:
Push: allocate / copy
Pop: free

You don't need more than that.
And push is add data to the stack and pop is remove data from the stack.
And kindly put your reply text outside the code tags.

[galaxy_virus]

The idea is:
Push: allocate / copy
Pop: free

You don't need more than that.
And push is add data to the stack and pop is remove data from the stack.
And kindly put your reply text outside the code tags.

Thanks for your reply. And I placed my post ouside code.

push : allocate

so there is no problem if we do malloc() for many times in push ( or add_data_to_stack) function () ??


My pop function looks like -

1) printing out all items
2) filling up NULL .. ( I am using this function as init() before using stack )
3) free memory

[Elysia]

Thanks for your reply. And I placed my post ouside code.

Yeah, that's good, but code should stay inside code tags. It was invented for the use of putting code inside.

push : allocate
so there is no problem if we do malloc() for many times in push ( or add_data_to_stack) function () ??

My pop function looks like -

1) printing out all items
2) filling up NULL .. ( I am using this function as init() before using stack )
3) free memory

Example:

void push(char* data)
{
    stack[++sp] = malloc(strlen(data) + 1); // Allocate
    strcpy(&stack[sp], data);
}

char* pop()
{
    char* temp = malloc( strlen(stack[sp]) );
    strcpy(temp, stack[sp]);
    free(&stack[sp--]);
    return temp;
}

Now we can talk about efficiency, but... let's leave that aside for now. This is just a basic example of how you might do.

[C_ntua]

You might want to add a check for if the stack is empty, since then pop() will cause a segmantation fault.

The performance issue is just about allocating and freeing memory all the time. Just keep that in mind for the feature. The alternative is to allocate once memory, lets say in an init() fucntion and free it with e delete() function. Another way is to just do char Stack[depth][stringDepth] and statically allocate memory.

[Elysia]

You might want to add a check for if the stack is empty, since then pop() will cause a segmantation fault.

Yes, I left that out on purpose.
It's only a basic example, not meant to be complete.