convert C++ vector into C

**meerajpatel** · 07-07-2009

first of all sorry for not posting properly since i am first time user. I just want to convert the below code into C from C++ vector. I tried to use structure and calloc or malloc but didn't work.

************************************************** **************

Code:

unsigned int current_context = sim_cycle % cores[core_num].context_ids.size();
 int disp_context_id = cores[core_num].context_ids[current_context]; /* the ID of the context currently being examined */
 std::vector<int> contexts_left(cores[core_num].context_ids);
 
disp_context_id = contexts_left[current_context];
  if(contexts[disp_context_id].ROB_num == 0)
  {
   //if there are no more instructions waiting dispatch for this thread, try another thread
   contexts_left.erase(contexts_left.begin()+current_context);
   if(contexts_left.empty())
    break;
   current_context%=contexts_left.size();
   continue;
  }

**dwks** · 07-07-2009

Why do you need a C-style array? Unless you're tied to a C interface, you can probably do just about anything you would want to do with a C++ vector directly.

But if you insist . . . you could use something like this.

Code:

/** Converts a C++ vector into a dynamically allocated array.

    It is the caller's responsibility to free the returned array with delete[].
*/
int *vector_to_array(const std::vector<int> &v) {
    int *a = new int[v.size()];
    for(std::vector<int>::size_type x = 0; x < v.size(); x ++) {
        a[x] = v[x];
    }
    return a;
}

**quzah** · 07-08-2009

C++ forum that way... -->

Quzah.

**Cactus_Hugger** · 07-08-2009

;-)

Code:

template<typename T>
T *vector_to_array(const std::vector<T> &v)
{
    T *arr = new T[v.size()];
    std::copy(v.begin(), v.end(), arr);
    return arr;
}

(Note that if you ever use exceptions, neither of these snippets are exception-safe.)

**meerajpatel** · 07-08-2009

oh I think I didn't explain it right. I need to use it in C program and not convert just C++ vector to array. I need C code as I am using C copiler (GCC) and this structure will be the part of my C program. so I tried to use structure like this.

Code:

struct contexts_left{
int disp_context_id;
};

if(contexts[disp_context_id].ROB_num == 0)
  {
   //if there are no more instructions waiting dispatch for this thread, try another thread
   contexts_left.erase(contexts_left.begin()+current_context);
   if(contexts_left.empty())
    break;
   current_context%=contexts_left.size();
   continue;
  }

but the above way of declaring array "contexts_left" was still giving error that contexts_left is undeclared. Also I tried calloc and malloc function to allocate memory like this,

Code:

current_context = (struct contexts_left *)malloc(sizeof(struct contexts_left))

but still can't figure out what is it that I am missing.
It might be really easy to ask but I have just started to use C programing and not so much familier with it.

Thank You for your response.

**ಠ_ಠ** · 07-08-2009

so you want to simulate a vector in C?

**meerajpatel** · 07-08-2009

not the vector but correct C code that is equivalent to vector.

**tabstop** · 07-08-2009

Originally Posted by meerajpatel

not the vector but correct C code that is equivalent to vector.

What, you mean:

Code:

/* initialize */
myvector = malloc(how_many * sizeof(*myvector));

/* grow */
temp = realloc(now_how_many * sizeof(*myvector));
if (temp == NULL) {
    printf("hack cough die\n");
} else {
    myvector = temp;
}

sort of thing? (I mean, obviously that's probably not everything you would want, but.)

**meerajpatel** · 07-08-2009

like I have this code here

Code:

unsigned int current_context = sim_cycle % cores[core_num].context_ids.size();
 int disp_context_id = cores[core_num].context_ids[current_context];  std::vector<int> contexts_left(cores[core_num].context_ids);
 
disp_context_id = contexts_left[current_context];
  if(contexts[disp_context_id].ROB_num == 0)
  {
   //if there are no more instructions waiting dispatch for this thread, try another thread
   contexts_left.erase(contexts_left.begin()+current_context);
   if(contexts_left.empty())
    break;
   current_context%=contexts_left.size();
   continue;
  }

In this code, contexts_left is the array and it has list of contexts (disp_context_id). current_context is the index that points to any particular disp_context_id. current_context is initialized with next context every cycle. and no of contexts in array( that is size of array) is the number that we can specify at a time of simulation.

now the if statement is just an example of condition that if that condition is true then we need to go to next context so it erases that particular context and next context will take place of it. so basically all context next to the erased one will move up by one location. current_context will be same during this time.

so to use this type of structure in C program, I tried to use structure as I mentioned previously, but didn't work.

I really appreciate help.

Thank You.

**tabstop** · 07-08-2009

Originally Posted by meerajpatel

like I have this code here

Code:

unsigned int current_context = sim_cycle % cores[core_num].context_ids.size();
 int disp_context_id = cores[core_num].context_ids[current_context];  std::vector<int> contexts_left(cores[core_num].context_ids);
 
disp_context_id = contexts_left[current_context];
  if(contexts[disp_context_id].ROB_num == 0)
  {
   //if there are no more instructions waiting dispatch for this thread, try another thread
   contexts_left.erase(contexts_left.begin()+current_context);
   if(contexts_left.empty())
    break;
   current_context%=contexts_left.size();
   continue;
  }

In this code, contexts_left is the array and it has list of contexts (disp_context_id). current_context is the index that points to any particular disp_context_id. current_context is initialized with next context every cycle. and no of contexts in array( that is size of array) is the number that we can specify at a time of simulation.

now the if statement is just an example of condition that if that condition is true then we need to go to next context so it erases that particular context and next context will take place of it. so basically all context next to the erased one will move up by one location. current_context will be same during this time.

so to use this type of structure in C program, I tried to use structure as I mentioned previously, but didn't work.

I really appreciate help.

Thank You.

So you'll have to write an erase function.

**Zlatko** · 07-09-2009

Hello.
Lets see if we're clear on what you want.
I think you want an abstract data type which acts like a C++ vector, but you want to use it in C so that you can write things like:

Vector* v = Vector_new(int elementSize, int initialCapacity);
or maybe even
Vector* v = Vector_new(int elementSize, int initialCapacity, copyConstructorFunctionPtr, destructorFunctionPtr);

and
Vector_pushBack(Vector* v, void* someData);
Vector_getElementAt(Vector* v, int index, void** someData)
Vector_eraseElementAt(Vector* v, int index);

Sorry, if I'm restating what other posters already have.

Start by summarizing the operations you want. Decide if your vector needs to hold structure elements or just primitive data types (int, double, pointer).

Then decide how you want to store the data in the vector. An array is probably a good choice, unless you're doing a lot of deletion from the anywhere except the end. But, if that's the case, you wouldn't have used the C++ vector in the first place.

Then for each operation, write the code to manipulate the internal data structure. It's not hard, but you need to organize your thoughts.

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