prop_string_size
size_t prop_string_size(prop_string_t);
const size_t string_size = prop_string_size(v);
len = prop_string_size(str);
len = prop_string_size(str);
proto_len = prop_string_size(obj);
args->propsize = prop_string_size(propval) + 1;
ATF_REQUIRE(prop_string_size(s1) == strlen(const_string1));
ATF_REQUIRE(prop_string_size(s2) == strlen(const_string2));