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

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.

5 Answers

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);

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

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 }

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

malloc or calloc

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