// (1) #define JSON_CATCH_USER(exception) /* value */ // (2) #define JSON_THROW_USER(exception) /* value */ // (3) #define JSON_TRY_USER /* value */
Controls how exceptions are handled by the library.
#!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 exceptions. The macro is always followed by a scope.#!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.#!cpp try calls inside the library. It has no arguments and is always followed by a scope.exception (in) : an exception type
By default, the macros map to their respective C++ keywords:
#define JSON_CATCH_USER(exception) catch(exception) #define JSON_THROW_USER(exception) throw exception #define JSON_TRY_USER try
When exceptions are switched off, the #!cpp try block is executed unconditionally, and throwing exceptions is replaced by calling std::abort to make reaching the #!cpp throw branch abort the process.
#define JSON_THROW_USER(exception) std::abort() #define JSON_TRY_USER if (true) #define JSON_CATCH_USER(exception) if (false)
??? example
The code below switches off exceptions and creates a log entry with a detailed error message in case of errors.
```cpp
#include <iostream>
#define JSON_TRY_USER if(true)
#define JSON_CATCH_USER(exception) if(false)
#define JSON_THROW_USER(exception) \
{std::clog << "Error in " << __FILE__ << ":" << __LINE__ \
<< " (function " << __FUNCTION__ << ") - " \
<< (exception).what() << std::endl; \
std::abort();}
#include <nlohmann/json.hpp>
```