NAME¶

std::throw_with_nested - std::throw_with_nested

Synopsis¶

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

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& nestedException) {
print_exception(nestedException, 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);
}
}

Possible output:¶

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

See also¶

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