How can I implement an array whose size is not known at compile time in C89? [closed]

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Sorry, I'm a bit of a newbie to C and was wondering how you could create an array whose size is not known at compile time before the C99 standard was introduced.

Answer 1

It's very easy. For example, if you want to create a variable length 1D int array, do the following. First, declare a pointer to type int:

int *pInt;

Next, allocate memory for it. You should know how many elements you will need (NUM_INTS):

pInt = malloc(NUM_INTS * sizeof(*pInt));

Don't forget to free your dynamically allocated array to prevent memory leaks:

free(pInt);

Answer 2

Use malloc function from stdlib.h to create a dynamic array object.

Answer 3

the ordinary way would be to allocate the data on the heap

  #include <stdlib.h>
  void myfun(unsigned int n) {
    mytype_t*array = (mytype_t*)malloc(sizeof(mytype_t) * n);
    // ... do something with the array
    free(array);
  }

you could also allocate on the stack (so you don't need to free manually):

  #include <alloca.h>
  void myfun(unsigned int n) {
    mytype_t*array = (mytype_t*)alloca(sizeof(mytype_t) * n);
    // ... do something with the array
  }

Answer 4

You can do this by dynamic memory allocation. Use malloc function.

Answer 5

malloc or calloc

YourType* ptr = malloc(sizeof(YourType)*NumberOfItemsYouNeed)