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Difference between revisions of "cpp/error/nested exception"

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{{cpp/title|nested_exception}}
 
{{cpp/title|nested_exception}}
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{{cpp/error/sidebar}}
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{{cpp/error/navbar}}
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{{ddcl | header=exception | notes={{mark c++11 feature}} | 1=
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{{ddcl|header=exception|since=c++11|1=
 
class nested_exception;
 
class nested_exception;
 
}}
 
}}
  
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{{tt|std::nested_exceptions}} 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.   
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{{tt|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===
 
===Member functions===
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{{dcl list begin}}
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{{dsc begin}}
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{{dcl list mem ctor | cpp/error/nested_exception/nested_exception | constructs a nested_exception}}
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{{dsc mem ctor|cpp/error/nested_exception/nested_exception|constructs a nested_exception}}
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{{dcl list mem vdtor | cpp/error/nested_exception/~nested_exception | destructs a nested exception}}
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{{dsc mem vdtor|cpp/error/nested_exception/~nested_exception|destructs a nested exception}}
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{{dcl list mem fun | cpp/error/nested_exception/operator{{=}} | replaces the contents of a nested_exception}}
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{{dsc mem fun|cpp/error/nested_exception/operator{{=}}|replaces the contents of a nested_exception}}
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{{dcl list mem fun | cpp/error/nested_exception/rethrow_nested | throws the stored exception}}
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{{dsc mem fun|cpp/error/nested_exception/rethrow_nested|throws the stored exception}}
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{{dcl list mem fun | cpp/error/nested_exception/nested_ptr | obtains a pointer to the stored exception}}
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{{dsc mem fun|cpp/error/nested_exception/nested_ptr|obtains a pointer to the stored exception}}
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{{dcl list end}}
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{{dsc end}}
 +
 
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===Non-member functions===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/error/dsc throw_with_nested}}
 +
{{dsc inc|cpp/error/dsc rethrow_if_nested}}
 +
{{dsc end}}
  
 
===Example===
 
===Example===
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{{example cpp
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{{include|cpp/error/example_nested_exception}}
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| Demonstrates construction and recursion through a nested exception object
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| code=
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#include <iostream>
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#include <stdexcept>
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#include <exception>
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#include <string>
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#include <fstream>
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// prints the explanatory string of an exception.
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===See also===
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// if the exception is nested, recurses to print the explanatory of the exception it holds
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{{dsc begin}}
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void print_exception(const std::exception& e, int level =  0)
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{{dsc inc|cpp/error/dsc exception_ptr}}
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{
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{{dsc inc|cpp/error/dsc throw_with_nested}}
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    std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\n';
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{{dsc inc|cpp/error/dsc rethrow_if_nested}}
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    try {
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{{dsc end}}
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        std::rethrow_if_nested(e);
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    } catch(const std::exception& e) {
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        print_exception(e, level+1);
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    } catch(...) {}
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}
+
  
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// sample function that catches an exception and wraps it in a nested exception
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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void open_file(const std::string& s)
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{
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    try {
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        std::ifstream file(s);
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        file.exceptions(std::ios_base::failbit);
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    } catch(...) {
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        std::throw_with_nested( std::runtime_error("Couldn't open " + s) );
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    }
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}
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−
 
+
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// sample function that catches an exception and wraps it in a nested exception
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void run()
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{
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    try {
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        open_file("nonexistent.file");
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    } catch(...) {
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        std::throw_with_nested( std::runtime_error("run() failed") );
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    }
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}
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// runs the sample function above and prints the caught exception
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int main()
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{
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    try {
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        run();
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    } catch(const std::exception& e) {
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        print_exception(e);
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    }
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}
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| output=
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exception: run() failed
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exception: Couldn't open nonexistent.file
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  exception: basic_ios::clear
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}}
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===See also===
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−
{{dcl list begin}}
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{{dcl list template | cpp/error/exception/dcl list exception_ptr}}
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{{dcl list end}}
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Latest revision as of 01:31, 1 September 2023

 
C++
 
Diagnostics library
 
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.

Contents

[edit] Member functions

 constructs a nested_exception
(public member function)
[virtual]
 destructs a nested exception
(virtual public member function)
replaces the contents of a nested_exception
(public member function)
throws the stored exception
(public member function)
obtains a pointer to the stored exception
(public member function)

[edit] Non-member functions

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

[edit] Example

[edit]

Demonstrates construction and recursion through a nested exception object.

Run this code
#include <exception>
#include <fstream>
#include <iostream>
#include <stdexcept>
#include <string>
 
// 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

[edit] See also

(C++11)
 shared pointer type for handling exception objects
(typedef) [edit]
(C++11)
 throws its argument with std::nested_exception mixed in
(function template) [edit]
(C++11)
 throws the exception from a std::nested_exception
(function template) [edit]
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