sd_journal_get_catalog_for_message_id() works similar to sd_journal_get_catalog() but the entry is looked up by the specified message ID (no open journal context is necessary for this), and no field substitution is performed.
sd_journal_get_catalog() and sd_journal_get_catalog_for_message_id() return 0 on success or a negative errno-style error code. If no matching message catalog entry is found, -ENOENT is returned.
On successful return, ret points to a new string, which must be freed with free(3).
Function sd_journal_get_catalog() is thread-agnostic and only a single specific thread may operate on a given object during its entire lifetime. It's safe to allocate multiple independent objects and use each from a specific thread in parallel. However, it's not safe to allocate such an object in one thread, and operate or free it from any other, even if locking is used to ensure these threads don't operate on it at the very same time.
Function sd_journal_get_catalog_for_message_id() is are thread-safe and may be called in parallel from multiple threads.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.