C++语法之function-try-block

C++里边有个看着比较怪异的语法，叫做“function-try-block”。见下面代码示例中的普通函数和构造函数的用法。另外析构函数也支持这种用法。

个人不觉得这个用法很赞，主要是因为它的行为比较复杂，对于普通函数和构造函数析构函数在到达catch-block结尾时候的行为不太一致，可以认为是比较坑猿的。

另外这个特性在C++98的时候就已经存在了，所以示例代码特意没有使用C++11或更高版本的语法。

#include <iostream>
#include <exception>
 
// Demonstration of function-try-block
// See Also: 
//   https://en.cppreference.com/w/cpp/language/function-try-block
 
class SomeException : public std::exception
{
private:
    std::string message;
 
public:
    SomeException (const char * msg) : message(msg)
    {
    }
 
    virtual ~SomeException() _NOEXCEPT /* use noexcept in C++11 */
    {
    }
 
    virtual const char* what() const _NOEXCEPT /* use noexcept in C++11 */ {
        return message.c_str();
    }
};
 
 
void foo () {
    std::cout << "simple foo function" << std::endl;
}
 
void bar() {
    std::cout << "evil bar function" << std::endl;
    throw SomeException("Some exception in bar");
}
 
void tryfunction (int i=0)
try {
    foo();
    bar();
} catch(const std::exception & e) {
    std::cout << "something was wrong - " << e.what() << std::endl;
    std::cout << "i = " << i << std::endl;
}
 
 
class EvilBase
{
public:
    EvilBase () {
        throw SomeException("dark side of the force");
    }
 
    virtual ~EvilBase () {
    }
};
 
class InnocentDerived : public EvilBase
{
public:
    InnocentDerived() try : EvilBase(), m(1)
    {
        // other initializations
    } catch (const std::exception & e) {
        std::cerr << "what is the problem? " << e.what() << std::endl;
    } // the current exception is rethrown here
 
private:
    int m;
};
 
int main() {
    tryfunction();
 
    InnocentDerived d;
}

讲代码保存为文件tryfunction.cpp，编译命令如下:

`$ g++ -std=c++98 tryfunction.cpp -o ./a1`