1# Supported Macros 2 3Some aspects of the library can be configured by defining preprocessor macros before including the `json.hpp` header. 4 5## `JSON_ASSERT(x)` 6 7The default value is `#!cpp assert(x)`. 8 9## `JSON_CATCH_USER(exception)` 10 11This macro overrides `#!cpp catch` calls inside the library. The argument is the type of the exception to catch. As of version 3.8.0, the library only catches `std::out_of_range` exceptions internally to rethrow them as [`json::out_of_range`](../home/exceptions.md#out-of-range) exceptions. The macro is always followed by a scope. 12 13See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example. 14 15## `JSON_NOEXCEPTION` 16 17Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`. 18When defining `JSON_NOEXCEPTION`, `#!cpp try` is replaced by `#!cpp if (true)`, 19`#!cpp catch` is replaced by `#!cpp if (false)`, and `#!cpp throw` is replaced by `#!cpp std::abort()`. 20 21The same effect is achieved by setting the compiler flag `-fno-exceptions`. 22 23## `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK` 24 25When defined, the library will not create a compile error when a known unsupported compiler is detected. This allows to use the library with compilers that do not fully support C++11 and may only work if unsupported features are not used. 26 27## `JSON_THROW_USER(exception)` 28 29This macro overrides `#!cpp throw` calls inside the library. The argument is the exception to be thrown. Note that `JSON_THROW_USER` should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior. 30 31See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example. 32 33## `JSON_TRY_USER` 34 35This macro overrides `#!cpp try` calls inside the library. It has no arguments and is always followed by a scope. 36 37See [Switch off exceptions](../home/exceptions.md#switch-off-exceptions) for an example. 38 39## `JSON_USE_IMPLICIT_CONVERSIONS` 40 41When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. 42 43??? example 44 45 This is an example for an implicit conversion: 46 47 ```cpp 48 json j = "Hello, world!"; 49 std::string s = j; 50 ``` 51 52 When `JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`, the code above does no longer compile. Instead, it must be written like this: 53 54 ```cpp 55 json j = "Hello, world!"; 56 auto s = j.get<std::string>(); 57 ``` 58 59## `NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)` 60 61This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object. 62 63The macro is to be defined inside of the class/struct to create code for. Unlike [`NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`](#nlohmann_define_type_non_intrusivetype-member), it can access private members. 64The first parameter is the name of the class/struct, and all remaining parameters name the members. 65 66See [Simplify your life with macros](arbitrary_types.md#simplify-your-life-with-macros) for an example. 67 68## `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)` 69 70This macro can be used to simplify the serialization/deserialization of types if (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object. 71 72The macro is to be defined inside of the namespace of the class/struct to create code for. Private members cannot be accessed. Use [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](#nlohmann_define_type_intrusivetype-member) in these scenarios. 73The first parameter is the name of the class/struct, and all remaining parameters name the members. 74 75See [Simplify your life with macros](arbitrary_types.md#simplify-your-life-with-macros) for an example. 76 77## `NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)` 78 79This macro simplifies the serialization/deserialization of enum types. See [Specializing enum conversion](enum_conversion.md) for more information. 80