Upgrading from 1.x

This chapter lists the backwards incompatible changes introduced in Jansson 2.0, and the steps that are needed for upgrading your code.

The incompatibilities are not dramatic. The biggest change is that all decoding functions now require and extra parameter. Most programs can be modified to work with 2.0 by adding a 0 as the second parameter to all calls of json_loads(), json_loadf() and json_load_file().


Jansson 2.0 is backwards incompatible with the Jansson 1.x releases. It is ABI incompatible, i.e. all programs dynamically linking to the Jansson library need to be recompiled. It’s also API incompatible, i.e. the source code of programs using Jansson 1.x may need modifications to make them compile against Jansson 2.0.

All the 2.x releases are guaranteed to be backwards compatible for both ABI and API, so no recompilation or source changes are needed when upgrading from 2.x to 2.y.

List of Incompatible Changes

Decoding flags

For future needs, a flags parameter was added as the second parameter to all decoding functions, i.e. json_loads(), json_loadf() and json_load_file(). All calls to these functions need to be changed by adding a 0 as the second argument. For example:

/* old code */
json_loads(input, &error);

/* new code */
json_loads(input, 0, &error);
Underlying type of JSON integers

The underlying C type of JSON integers has been changed from int to the widest available signed integer type, i.e. long long or long, depending on whether long long is supported on your system or not. This makes the whole 64-bit integer range available on most modern systems.

jansson.h has a typedef json_int_t to the underlying integer type. int should still be used in most cases when dealing with smallish JSON integers, as the compiler handles implicit type coercion. Only when the full 64-bit range is needed, json_int_t should be explicitly used.

Maximum encoder indentation depth
The maximum argument of the JSON_INDENT() macro has been changed from 255 to 31, to free up bits from the flags parameter of json_dumps(), json_dumpf() and json_dump_file(). If your code uses a bigger indentation than 31, it needs to be changed.
Unsigned integers in API functions
Version 2.0 unifies unsigned integer usage in the API. All uses of unsigned int and unsigned long have been replaced with size_t. This includes flags, container sizes, etc. This should not require source code changes, as both unsigned int and unsigned long are usually compatible with size_t.