diff options
Diffstat (limited to 'docs/reference.rst')
| -rw-r--r-- | docs/reference.rst | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/docs/reference.rst b/docs/reference.rst index 93aae8b..0db8e43 100644 --- a/docs/reference.rst +++ b/docs/reference.rst @@ -24,6 +24,8 @@ PB_NO_ERRMSG Disables the support for error messages; only err Decreases the code size by a few hundred bytes. PB_BUFFER_ONLY Disables the support for custom streams. Only supports encoding to memory buffers. Speeds up execution and decreases code size slightly. +PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead of void\*\*) for callback fields. This was the + default until nanopb-0.2.1. ============================ ================================================================================================ The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow raising some datatype limits to suit larger messages. @@ -122,14 +124,16 @@ Part of a message structure, for fields with type PB_HTYPE_CALLBACK:: typedef struct _pb_callback_t pb_callback_t; struct _pb_callback_t { union { - bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void *arg); - bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, const void *arg); + bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg); + bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg); } funcs; void *arg; }; -The *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. +A pointer to the *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. + +Previously the function received just the value of *arg* instead of a pointer to it. This old behaviour can be enabled by defining *PB_OLD_CALLBACK_STYLE*. When calling `pb_encode`_, *funcs.encode* is used, and similarly when calling `pb_decode`_, *funcs.decode* is used. The function pointers are stored in the same memory location but are of incompatible types. You can set the function pointer to NULL to skip the field. |