C / C++ / MFC

Stefan_Lang wrote:

Calling it an idiom may be misleading - it may be commonly used, but it is most
certainly not a recommended practice, and technically not even supported by the
standard.

Stefan_Lang wrote:

in C++, there are much better ways to create dynamic arrays. In fact you have
to look no further than std::vector .

Stefan_Lang wrote:

In any case, you have to be very careful about allocating and deallocating

Stefan_Lang wrote:

but it's also possible to define an instance of that type on the stack instead
if you know the required size at compile time.

jschell wrote:

First part is an opinion but feel free to substantiate it.

jschell wrote:

Just as you must be careful about anything involving pointers and memory in C/C++.

jschell wrote:

<layer>Except that is exactly the point - it isn't known at compile time.

Stefan_Lang wrote:

From a C++ programmers point of view it's terribad

Stefan_Lang wrote:

However, using such structs breaks expectations...,

Stefan_Lang wrote:

This information can only be passed by comments

Stefan_Lang wrote:

not via source code, and the compiler has no way of telling whether you're doing
it right.

Stefan_Lang wrote:

Managing pointers and avoiding leaks is easy in comparison, and quite easily
managed by a decent set of guidelines.

Stefan_Lang wrote:

So you could define a sufficiently large memory block an the stack to store
values within that function.

struct MessagData
{
    DWORD dwSize;
    BYTE byData[1];
}
char chReadData[100];
// fill chReadData with the information from external source
MessagData* pMessagData = reinterpret_cast<MessagData*>(chReadData);
// The reinterpret_cast operation tells the compiler you know that
// the structure of chReadData is the same as your structure.

Rahul from Poona wrote:

So following line is not applicable here

struct MessagData
{
    DWORD dwSize;
    BYTE byData[1];
}
char chReadData[100];
int dwNumberRead;
// fill chReadData with the information from external source
// and set dwNumberRead to the length of the data

// now allocate a structure that is big enough to hold this data
// copy the data into the structure and set its length member variable
MessagData* pMessagData = (MessagData*)new BYTE[sizeof(MessagData) + dwNumberRead];
memcpy(pMessagData->byData, chReadData, dwNumberRead);
pMessagData->dwSize = dwNumberRead;

Rahul from Poona wrote:

I m reading some data from device whose length I dont know at compile so I made
a structure as of following type to store data