on-the-heap.c

#include <stdlib.h>

typedef struct {
  char *name;
  int length;
} message_t;

int main(void) {
  message_t *messages;
  int amount = 50;
  messages = (message_t *) malloc(sizeof(message_t) * amount);
  /* do stuff here */
  free(messages);
  return 0;
}

on-the-stack.c

#include <stdlib.h>

typedef struct {
  char *name;
  int length;
} message_t;

int main(void) {
  message_t messages[50];
  /* do stuff here */
  return 0;
}

return-array-of-structs.c

#include <assert.h>
#include <stdlib.h>

typedef struct {
  char *name;
  int length;
} message_t;

/* Dynamically allocates an "amount" amount of messages and
   returns the pointer. The client must later call
   messages_free() on the pointer to avoid a memory leak. */
message_t* messages_init(int amount) {
  message_t *messages =
    (message_t *) malloc(sizeof(message_t) * amount);
  assert(messages != NULL);
  /* Do stuff here, if you want */
  return messages;
}

/* Frees the messages allocated by messages_init(). Every
   messages_init() call needs to be paired with a
   messages_free() call. */
void messages_free(message_t *messages) {
  free(messages);
}

int main(void) {
  message_t *messages = messages_init(50);
  int i;
  for (i = 0; i < 50; i++) {
    message_t *message = &messages[i];
    message->length = 10;
    /* Other stuff */
  }
  free_messages(messages);
  return 0;
}