realloc in C

Resizing a heap allocation, growing an array.

#include <stdlib.h>

int *grow(int *items, int old_n, int new_n) {
    int *bigger = realloc(items, new_n * sizeof(int));
    if (bigger == NULL) {
        free(items);
        return NULL;
    }
    for (int i = old_n; i < new_n; i++)
        bigger[i] = 0;
    return bigger;
}

How it works

1. realloc returns a possibly-moved larger block.
2. On failure the old block is freed to avoid a leak.
3. New slots are zeroed before use.

Keywords and builtins used here

• NULL
• for
• grow
• if
• int
• return
• sizeof

The run, in numbers

Lines

12

Characters to type

235

Tokens

77

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 49 seconds.

Type this snippet

Step 3 of 5 in Dynamic memory, step 12 of 25 in Pointers & memory.

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