membuf_t is a growable continuous in-memory buffer. It also support "local buffer" to use stack memory efficiently.
membuf_t buf; char on_stack_buffer[16];
membuf_init_local(&buf, on_stack_buffer, sizeof(on_stack_buffer));
membuf_append_text(&buf, "0123456789", 10); // uses stack buffer
membuf_append_text(&buf, "ABCDEF", 6); // still uses stack buffer
membuf_append_zeros(&buf, 1); // now it uses heap buffer
printf("%s\n", buf.data); // will prints "0123456789ABCDEF"
membuf_uninit(&buf);