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JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER

// (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.

  1. This macro overrides 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.
  2. This macro overrides 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.
  3. This macro overrides try calls inside the library. It has no arguments and is always followed by a scope.

Parameters

exception (in)
an exception type

Default definition

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 try block is executed unconditionally, and throwing exceptions is replaced by calling std::abort to make reaching the 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)

Examples

Example

The code below switches off exceptions and creates a log entry with a detailed error message in case of errors.

#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>

See also

Version history

  • Added in version 3.1.0.

Last update: September 18, 2022