std::throw_with_nested

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated in C++20)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)
launder (C++17)

 

Error handling

Exception handling exception uncaught_exceptionuncaught_exceptions (until C++20)(C++17) exception_ptr (C++11) make_exception_ptr (C++11) current_exception (C++11) rethrow_exception (C++11) nested_exception (C++11) throw_with_nested (C++11) rethrow_if_nested (C++11) Exception handling failures terminate terminate_handler get_terminate (C++11) set_terminate bad_exception unexpected (until C++17) unexpected_handler (until C++17) get_unexpected (C++11)(until C++17) set_unexpected (until C++17) Contracts contract_violation (C++20)

Exception categories logic_error invalid_argument domain_error length_error out_of_range runtime_error range_error overflow_error underflow_error tx_exception (TM TS) Error codes Error codes errno Assertions assert system_error facility error_category (C++11) generic_category (C++11) system_category (C++11) error_condition (C++11) errc (C++11) error_code (C++11) system_error (C++11)

 

Defined in header <exception>
template< class T > [[noreturn]] void throw_with_nested( T&& t );		(since C++11)

If std::decay<T>::type is a non-final non-union class type that is neither std::nested_exception nor derived from std::nested_exception, throws an exception of an unspecified type that is publicly derived from both std::nested_exception and from std::decay<T>::type, and constructed from std::forward<T>(t). The default constructor of the nested_exception base class calls std::current_exception, capturing the currently handled exception object, if any, in a std::exception_ptr.

Otherwise, throws std::forward<T>(t).

Requires that std::decay<T>::type is CopyConstructible

Parameters

t

-

the exception object to throw

Return value

(none)

Example

Demonstrates construction and recursion through a nested exception object

Run this code

#include <iostream>
#include <stdexcept>
#include <exception>
#include <string>
#include <fstream>
 
// prints the explanatory string of an exception. If the exception is nested,
// recurses to print the explanatory of the exception it holds
void print_exception(const std::exception& e, int level =  0)
{
    std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\n';
    try {
        std::rethrow_if_nested(e);
    } catch(const std::exception& e) {
        print_exception(e, level+1);
    } catch(...) {}
}
 
// sample function that catches an exception and wraps it in a nested exception
void open_file(const std::string& s)
{
    try {
        std::ifstream file(s);
        file.exceptions(std::ios_base::failbit);
    } catch(...) {
        std::throw_with_nested( std::runtime_error("Couldn't open " + s) );
    }
}
 
// sample function that catches an exception and wraps it in a nested exception
void run()
{
    try {
        open_file("nonexistent.file");
    } catch(...) {
        std::throw_with_nested( std::runtime_error("run() failed") );
    }
}
 
// runs the sample function above and prints the caught exception
int main()
{
    try {
        run();
    } catch(const std::exception& e) {
        print_exception(e);
    }
}

Output:

exception: run() failed
 exception: Couldn't open nonexistent.file
  exception: basic_ios::clear

See also

nested_exception (C++11)	a mixin type to capture and store current exceptions (class)
rethrow_if_nested (C++11)	throws the exception from a std::nested_exception (function template)