c++ lambda表达式问题

Question

下面这段代码在ubuntu g++ 4.6.3 可以正常运行，在g++ 5.2 中运行正常。但是在centos g++ 4.8.5中运行失败，但是把lambda表达式注释之后就可以正常运行，这个和编译器有关吗？

// 这是一个工具类
class ScopeGuard
{
public:
    explicit ScopeGuard(std::function<void ()> onExitScope)
    :onExitScope_(onExitScope)
    {

    }

    ~ScopeGuard()
    {
        onExitScope_();
    }
private:
    std::function<void ()> onExitScope_;
};

下面程序是用来解压的程序，但是在centos中会解压失败。

    // 上面还有类似的几个lambda表达式
    int dstLen = 10 * 1024 * 1024;
    char *dstBuf = new char[dstLen];
        // 把下面一行注释掉就可以正确解压，只要函数内有一个这样的表达式就会解压失败
    ScopeGuard guard([&](){if (dstBuf) delete[] dstBuf; dstBuf=NULL;});

        // src 是解压前的数据，fileLen是数据长度
    int err = uncompress((Bytef *)dstBuf, (uLongf*)&dstLen, (Bytef*)src, fileLen);

    if (err != Z_OK)
    {
        cout<<"uncompress error..."<<err<<endl;
        return false;
    }

请问，是我的lambda方式用错了还是编译器的bug？

Answer 1

What is the return value when decompression fails? lambda Support feels like there should be no problem with this. gcc 4.5 has started to support lambda. gcc 4.8.5 is already a relatively stable version. The compiler's bug should be the last thing to consider...

Answer 2

When the guard object is destructed, it will call
[&](){if (dstBuf) delete[] dstBuf; dstBuf=NULL;}
The decompression failure you mentioned here means that the uncompress function return is not Z_OK like this? Or is there another problem with the program?

Also, [&]()mutable -->void {if (dstBuf) delete[] dstBuf; dstBuf=NULL;} this can be modified dstBuf. I haven't tested this, so I don't know if it is true.

Answer 3

Regarding the implementation of ScopeGuard, you can refer to Andrei Alexandrescu’s implementation in Facebook’s open source folly library

https://github.com/facebook/folly/blob/master/folly/ScopeGuard.h