Step 9 of 9

Challenge: a string builder

Building a long string with repeated strcat into a fixed buffer is how buffer overflows happen. Real C code uses a string builder: a struct that owns a growing heap buffer.

typedef struct {
    char *buf;   /* always '\0'-terminated once initialized */
    size_t len;  /* characters used, not counting '\0' */
    size_t cap;  /* bytes allocated */
} Builder;

Your turn: write the four functions:

• sb_init(b): allocate a small starting buffer (say 8 bytes) holding "". Return 0 on success, -1 if allocation fails.
• sb_append(b, s): append s, doubling cap as many times as needed. Return 0, or -1 if realloc fails (leave b unchanged then).
• sb_str(b): return the current string.
• sb_free(b): free the buffer and reset the fields.

Previous: Who owns what