c++ lambda expression confusion

Question

I feel confused about lambda in c++.Is it related to the compiler? The following code run correct in ubuntu g++ 4.6.3 and g++ 5.2. But when I run it in centos 4.8.5,the result is error.

// 
class ScopeGuard
{
 public:
    explicit ScopeGuard(std::function<void ()> onExitScope)
      :onExitScope_(onExitScope)
 {

 }

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

And there is a function to uncompress the data.

//
...
int dstLen = 10 * 1024 * 1024;
char *dstBuf = new char[dstLen];
// When I comment this line the err return Z_OK, otherwise return Z_BUFF_ERROR.
ScopeGuard guard([&](){if (dstBuf) delete[] dstBuf; dstBuf=NULL;});

// zlib function. 
int err = uncompress((Bytef *)dstBuf, (uLongf*)&dstLen, (Bytef*)src, fileLen);

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

The return value of function uncompress is Z_BUFF_ERR only when I run the code in centos g++ 4.8.5. when I annotate the ScopeGuard, It return Z_OK. — MiJia
– MiJia, Commented Jun 2, 2016 at 11:56
Also, CentOS is not a compiler; what's the actual compiler and its version? — Sebastian Redl
– Sebastian Redl, Commented Jun 2, 2016 at 11:56
When I run in centos with gcc version 4.8.5, the result is error. — MiJia
– MiJia, Commented Jun 2, 2016 at 11:59
Perhaps the call to new char[dstLen] fails in CentOS because you're requesting too much memory. Are you using the throwing version of new? — AndyG
– AndyG, Commented Jun 2, 2016 at 12:05

Sebastian Redl · Accepted Answer · 2016-06-02 12:06:37Z

1

This is most likely because of this: (uLongf*)&dstLen.

dstLen is an int, which is 32 bits and all current typical systems. uLongf, however, is an alias for unsigned long, which is 32 bits on Windows and 32-bit *nix systems, but 64 bits on 64-bit *nix systems.

It is not safe, and likely to do the wrong thing, to cast an int* to an uLongf*.

The solution is to make dstLen an uLongf and remove the cast.

answered Jun 2, 2016 at 12:06

Sebastian Redl

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2 Comments

MiJia Over a year ago

Yes, thanks a lot! I solved the problem with this method.

MiJia Over a year ago

The ubuntu is 32-bit,but centos is 64-bit

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