Howto base64 decode with C/C++ and OpenSSL

Someone asked for an example of decoding with OpenSSL on the Howto base64 encode with C/C++ and OpenSSL post. So here it is:

#include <string.h>

#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>

char *unbase64(unsigned char *input, int length);

int main(int argc, char **argv)
{
  char *output = unbase64("WU9ZTyEA\n\0", strlen("WU9ZTyEA\n\0"));
  printf("Unbase64: *%s*\n", output);
  free(output);
}

char *unbase64(unsigned char *input, int length)
{
  BIO *b64, *bmem;

  char *buffer = (char *)malloc(length);
  memset(buffer, 0, length);

  b64 = BIO_new(BIO_f_base64());
  bmem = BIO_new_mem_buf(input, length);
  bmem = BIO_push(b64, bmem);

  BIO_read(bmem, buffer, length);

  BIO_free_all(bmem);

  return buffer;
}