Unique file name using UUID - c

Question

I need to create some binary data files from Object Identifiers, which is a variable-length binary void* buffer, upto 64 bytes and can contain any bytes corresponding to non-printable characters as well. I can't use Object Identifier as my file name as it contains non-printable letters.
Any suggestions to create the unique filename. How can the UUID be derived or used in this case ?

Answer 1

You can convert the bytes into a hexadecimal string.
#define tohex(x) ("0123456789abcdef"[(x) & 0x0f])
char buf[129];
assert(objid_len <= 64);
for (int i = 0; i < objid_len; ++i) {
buf[2*i] = tohex(objid[i] >> 4);
buf[2*i+1] = tohex(objid[i]);
}
buf[2*objid_len] = '\0';
You can make the filenames have universal length by using a padding character that is outside the alphabet used to to represent the object id. If a shorter filename is desired, then a higher base could be used. For example, Base64.
const char * const base64str =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
#define tob64(x) base64str[(x) & 0x3f]
void objid_to_filename (const unsigned char *objid, int objid_len,
char *buf) {
memset(buf, '-', 88);
buf[88] = '\0';
int i = 0, j = 0;
int buflen = 4 * ((objid_len + 2)/3);
while (i < objid_len) {
unsigned x = 0;
x |= (i < objid_len) ? objid[i++] << 16 : 0;
x |= (i < objid_len) ? objid[i++] << 8 : 0;
x |= (i < objid_len) ? objid[i++] << 0 : 0;
buf[j++] = tob64(x >> 18);
buf[j++] = tob64(x >> 12);
buf[j++] = tob64(x >> 6);
buf[j++] = tob64(x >> 0);
}
int pad = (3 - (objid_len % 3)) % 3;
for (i = 0; i < pad; ++i) buf[buflen - 1 - i] = '=';
}