c++ - c++ design question try catch

Question

I have the following code in which dbh constructor may throw exception. The question I have is, dbh is declared inside try block. Will it be available after the catch? If yes, are there any other exceptions where the scope resolution is different than {} ? If not, what is the best design alternative?

status func(const char* field, char** value)
{
    try {
        dbhandler<recType> dbh(("dbName"),("table"));
    }
    catch (std::runtime_error &e) {
        LOG_ERR << e.what() << endl ;
        return false;
    }
    catch (...) {
        LOG_ERR << "Unknown exception" << endl ;
        return false;
    }

    rc = dbh.start("key",field, val);
    return rc;
}

Answer 1

抓到后能用吗？

不，它将在声明它的块的末尾被销毁，就像任何其他局部变量一样。

try {
    dbhandler<recType> dbh(("dbName"),("table")); 
}   // dbh.~dbhandler<recType>() is called to destroy dbh

最好的设计方案是什么？

dbh在块外声明try或将所有使用它的代码移到try块中。哪一个最有意义取决于您的具体用例。

在一些相关的说明中，如果您catch (...)应该重新抛出异常或终止应用程序：您不知道正在处理什么异常，并且通常您不知道继续执行是否安全。

Answer 2

根据您的功能代码，这样编写它很有意义：

status func(const char* field, char** value)
{
    try {
        dbhandler<recType> dbh(("dbName"),("table"));
        status rc = dbh.start("key",field, val);
        return rc;
    }
    catch (std::runtime_error &e) {
        LOG_ERR << e.what() << endl ;
        return false;
    }
    catch (...) {
        LOG_ERR << "Unknown exception" << endl ;
        return false;
    }
}