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std::filesystem::filesystem_error:: what

From cppreference.net
C++
Filesystem library
Classes
Functions
File types
filesystem_error
const char * what ( ) const noexcept override ;
(自 C++17 起)

返回一个说明性字节字符串。该说明字符串包含构造时传入的说明字符串。实现建议在返回的字符串中同时包含 path1() 和 path2() 的路径名（以原生格式）以及 std::system_error::what() 字符串。

参数

(无)

返回值

一个C风格的解释性字节字符串，包含构造时传入的解释性字符串。

示例

运行此代码 
#include <cstdio>
#include <filesystem>
#include <iostream>
#include <string_view>
namespace fs = std::filesystem;
void explain(std::string_view note, fs::filesystem_error const& ex)
{
    std::cout << note << " exception:\n"
              << "what(): " << ex.what() << '\n'
              << "path1(): " << ex.path1() << ", path2(): "
              << ex.path2() << "\n\n";
}
int main()
{
    try
    {
        std::filesystem::rename("/dev", "/null");
    }
    catch(fs::filesystem_error const& ex)
    {
        explain("fs::rename()", ex);
    }
    for (auto const path : {"/bool", "/bin/cat", "/bin/mouse"})
        try
        {
            std::filesystem::create_directory(path);
        }
        catch(fs::filesystem_error const& ex)
        {
            explain("fs::create_directory()", ex);
        }
}

可能的输出： 

fs::rename() exception:
what(): filesystem error: cannot rename: Permission denied [/dev] [/null]
path1(): "/dev", path2(): "/null"
fs::create_directory() exception:
what(): filesystem error: cannot create directory: Permission denied [/bool]
path1(): "/bool", path2(): ""
fs::create_directory() exception:
what(): filesystem error: cannot create directory: File exists [/bin/cat]
path1(): "/bin/cat", path2(): ""
fs::create_directory() exception:
what(): filesystem error: cannot create directory: Read-only file system [/bin/mouse]
path1(): "/bin/mouse", path2(): ""