使用C++异常的内存泄漏

我很难在C++11中编写一个小的文件句柄类。我知道STL中已经有很多东西可以实际处理文件，但出于学习目的，我想自己做这件事。

不幸的是，我似乎不明白，异常对C++程序的内存泄漏行为有什么影响，因为Valgrind告诉我，以下代码中有2个内存泄漏：

文件.h

#ifndef FILE_H
#define FILE_H
#include <iostream>
#include <memory>
#include <string>
#include <stdio.h>
class FileDeleter {
public:
    void operator()(FILE *p);
};
class File {
public:
    File(const std::string path);
private:
    const std::string _path;
    std::unique_ptr<FILE, FileDeleter> _fp;
};
#endif // FILE_H

文件.cpp

#include <cstring>
#include <iostream>
#include <stdexcept>
#include <utility>
#include <stdio.h>
#include "file.h"
void FileDeleter::operator()(FILE *p)
{
if (!p)
    return;
    if (fclose(p) == EOF)
        std::cerr << "FileDeleter: Couldn't close file" << std::endl;
}
File::File(const std::string path)
    : _path(std::move(path)),
      _fp(fopen(_path.c_str(), "a+"))
{
    if (!_fp)
        throw std::runtime_error("Couldn't open file");
}

main.cpp

#include <cstdlib>
#include "file.h"
int main()
{
    File my_file("/root/.bashrc");
    return EXIT_SUCCESS;
}

我确实故意选择打开/root/.bashrc，实际上是为了让File ctor抛出异常。如果我不扔到那里，瓦尔格里德会非常高兴。在使用异常时，我缺少什么？如何"正确"实现简单的文件句柄（异常安全）？

提前感谢！

注意：读/写操作仍然缺失，因为我已经在为基础知识而挣扎。

编辑#1：这是Valgrind的实际输出，使用--leak-check=full:

==7998== HEAP SUMMARY:
==7998==     in use at exit: 233 bytes in 3 blocks
==7998==   total heap usage: 5 allocs, 2 frees, 817 bytes allocated
==7998== 
==7998== 38 bytes in 1 blocks are possibly lost in loss record 1 of 3
==7998==    at 0x4C27CC2: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7998==    by 0x4EEC4F8: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x4EEDC30: char* std::string::_S_construct<char const*>(char const*, char const*, std::allocator<char> const&, std::forward_iterator_tag) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x4EEE047: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x40137D: main (in ../a.out)
==7998== 
==7998== 43 bytes in 1 blocks are possibly lost in loss record 2 of 3
==7998==    at 0x4C27CC2: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7998==    by 0x4EEC4F8: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x4EEDC30: char* std::string::_S_construct<char const*>(char const*, char const*, std::allocator<char> const&, std::forward_iterator_tag) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x4EEE047: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x400EBF: File::File(std::string) (in /home/frank/3Other/Code/Laboratory/c++/c++namedpipe/a.out)
==7998==    by 0x401390: main (in ../a.out)
==7998== 
==7998== 152 bytes in 1 blocks are possibly lost in loss record 3 of 3
==7998==    at 0x4C27730: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7998==    by 0x4E8F8F2: __cxa_allocate_exception (in /usr/lib/libstdc++.so.6.0.18)
==7998==    by 0x400E9B: File::File(std::string) (in /home/frank/3Other/Code/Laboratory/c++/c++namedpipe/a.out)
==7998==    by 0x401390: main (in ../a.out)
==7998== 
==7998== LEAK SUMMARY:
==7998==    definitely lost: 0 bytes in 0 blocks
==7998==    indirectly lost: 0 bytes in 0 blocks
==7998==      possibly lost: 233 bytes in 3 blocks
==7998==    still reachable: 0 bytes in 0 blocks
==7998==         suppressed: 0 bytes in 0 blocks

编辑#2：修复了Destructor中引发的异常。

编辑#3：删除了FileException类，改为使用std:：runtime_error。

编辑#4：在删除程序中添加了NULL检查。