std::throw_with_nested

STD：扔[医]带着[医]巢式

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

如果std::decay<T>::type是一个非最终的非联合类类型，两者都不是。std::nested_exception也不是从std::nested_exception引发一个未指定类型的异常，该异常是公开从这两个类型派生的。std::nested_exception和来自std::decay<T>::type，并由std::forward<T>(t)的默认构造函数。nested_exception基类调用std::current_exception中捕获当前处理的异常对象(如果有的话)。std::exception_ptr...

否则，抛出std::forward<T>(t)...

要求std::decay<T>::type是CopyConstructible...

参数

t	-	the exception object to throw

返回值

%280%29

例

演示通过嵌套异常对象进行的构造和递归。

二次

#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
    }
}

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产出：

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

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另见

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)

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