diff --git a/doc/apiref.rst b/doc/apiref.rst index 0ab2348..2a090e4 100644 --- a/doc/apiref.rst +++ b/doc/apiref.rst @@ -253,6 +253,24 @@ other. Moreover, trying to encode the values with any of the encoding functions will fail. The encoder detects circular references and returns an error status. +Scope Dereferencing +------------------- + +It is possible to use the ``json_auto_t`` type to automatically +dereference a value at the end of a scope. For example:: + + void function(void) { + json_auto_t *value = NULL; + value = json_string("foo"); + /* json_decref(value) is automatically called. */ + } + +This feature is only available on GCC and Clang. So if your project +has a portability requirement for other compilers, you should avoid +this feature. + +Additionally, as always, care should be taken when passing values to +functions that steal references. True, False and Null ==================== diff --git a/src/jansson.h b/src/jansson.h index 17a6e7a..b1a040a 100644 --- a/src/jansson.h +++ b/src/jansson.h @@ -112,6 +112,19 @@ void json_decref(json_t *json) json_delete(json); } +#if defined(__GNUC__) || defined(__clang__) +static JSON_INLINE +void json_decrefp(json_t **json) +{ + if(json) { + json_decref(*json); + *json = NULL; + } +} + +#define json_auto_t json_t __attribute__((cleanup(json_decrefp))) +#endif + /* error reporting */ diff --git a/test/suites/api/test_simple.c b/test/suites/api/test_simple.c index 8b56954..e461561 100644 --- a/test/suites/api/test_simple.c +++ b/test/suites/api/test_simple.c @@ -224,4 +224,17 @@ static void run_tests() json_incref(value); if(value->refcount != (size_t)-1) fail("refcounting null works incorrectly"); + +#ifdef json_auto_t + value = json_string("foo"); + { + json_auto_t *test = json_incref(value); + /* Use test so GCC doesn't complain it is unused. */ + if(!json_is_string(test)) + fail("value type check failed"); + } + if(value->refcount != 1) + fail("automatic decrement failed"); + json_decref(value); +#endif }