// sample code from commit.c of the Git repository (https://github.com/git)

struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name)

{

struct commit *c = lookup_commit_reference(sha1);

if (!c)

die(_("could not parse %s"), ref_name);

if (hashcmp(sha1, c->object.sha1)) {

warning(_("%s %s is not a commit!"),

ref_name, sha1_to_hex(sha1));

}

return c;

}