NAME

std::nested_exception - std::nested_exception

Synopsis

Defined in header <exception>
class nested_exception; (since C++11)

std::nested_exception is a polymorphic mixin class which can capture and store the
current exception, making it possible to nest exceptions of arbitrary types within
each other.

Member functions

constructor constructs a nested_exception
(public member function)
destructor destructs a nested exception
[virtual] (virtual public member function)
operator= replaces the contents of a nested_exception
(public member function)
rethrow_nested throws the stored exception
(public member function)
nested_ptr obtains a pointer to the stored exception
(public member function)

Non-member functions

throw_with_nested throws its argument with std::nested_exception mixed in
(C++11) (function template)
rethrow_if_nested throws the exception from a std::nested_exception
(C++11) (function template)

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: