C++核心准则​讨论：持有没有被句柄管理的资源时切勿抛出异常

Discussion: Never throw while holding a resource not owned by a handle

讨论：持有没有被句柄管理的资源时切勿抛出异常

Reason（原因）

That would be a leak.

这回引发资源泄露。

Example（注意）

void f(int i)
{
    FILE* f = fopen("a file", "r");
    ifstream is { "another file" };
    // ...
    if (i == 0) return;
    // ...
    fclose(f);
}

If i == 0 the file handle for a file is leaked. On the other hand, the ifstream for another file will correctly close its file (upon destruction). If you must use an explicit pointer, rather than a resource handle with specific semantics, use a unique_ptr or a shared_ptr with a custom deleter:

如果i == 0，则文件的句柄发生泄漏。另一方面，另一个文件的ifstream将正确关闭其文件（销毁时）。如果必须使用显式指针，而不是具有特定语义的资源句柄，请使用带有自定义删除器的unique_ptr或shared_ptr：

void f(int i)
{
    unique_ptr<FILE, int(*)(FILE*)> f(fopen("a file", "r"), fclose);
    // ...
    if (i == 0) return;
    // ...
}

Better:

更好的做法：

void f(int i)
{
    ifstream input {"a file"};
    // ...
    if (i == 0) return;
    // ...
}

Enforcement（实施建议）

A checker must consider all "naked pointers" suspicious. A checker probably must rely on a human-provided list of resources. For starters, we know about the standard-library containers, string, and smart pointers. The use of span and string_view should help a lot (they are not resource handles).

检查器必须将所有“暴露的指针”视为可疑。检查器可能必须依靠人工提供的资源列表。首先，我们了解标准库容器，字符串和智能指针。使用span和string_view应该会很有帮助（它们不是资源句柄）。

原文链接https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#discussion-never-throw-while-holding-a-resource-not-owned-by-a-handle