C function : how to pass a HANDLE as reference

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Hi,

I have a C application.

I want to build an init function which creates handles to events which will be used outside the init function

Something like this:

InitEvents(HANDLE hEvent1, char *Event1Name, HANDLE hEvent2, char *Event2Name)
{
hEvent1 = CreateEvent(..Event1Name...);
hEvent2 = CreateEvent(..Event2Name...);
}

void main()
{
HANDLE h1,h2;

InitEvents(h1, "ONE", h2, "TWO");

SetEvent(hEvent1);
}

How can i pass the HANDLES by reference so the created handles will be available in the main function?

Thanks!

What I have tried:

Declaring the InitEvents(HANDLE *hEvent1.....)
hEvent1 = CreateEvent(..Event1Name...);

Posted 15-May-19 3:58am

dj4400

Updated 15-May-19 4:53am

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OriginalGriff · Answer 1 · 2019-05-15T04:10:00

Solution 1

This is C, not C# or C++: you don't have references - all parameters in C are passed by value (i.e. a copy of the variable content is passed to the function, not the variable itself).

To pass a "reference" you pass the address of the variable and receive it in the function as a pointer:

C++

void InitEvents(HANDLE* phEvent1 ...)
   {
   *phEvent1 = CreateEvent(...);
   ...
   }
void main()
   {
   HANDLE h1, h2;
   InitEvents(&h1, ....);
   ...
   }

Posted 15-May-19 4:10am

OriginalGriff

Comments

dj4400 15-May-19 10:57am

Thanks!
It worked well with handles but i also want to create a shared memory in the init function
which means that the Init function will look like this
InitEvents(HANDLE hEvent1, char *Event1Name, HANDLE hEvent2, char *Event2Name,
unsigned char* pSharedMemory, char* SharedMemName )
{
hEvent1 = CreateEvent(..Event1Name...);
hEvent2 = CreateEvent(..Event2Name...);
CreateSharedMemory(..SharedMemName ..);
}

void main()
{
HANDLE h1,h2;
unsigned char pBuf[1000];
InitEvents(h1, "ONE", h2, "TWO", pBuf, "SHARED");

SetEvent(hEvent1);
memcpy(pBuf,SomeData, DataLen);
}
I tried passing **char and calling Init with &pBuf

CPallini 15-May-19 13:41pm

dj forgot to upvote your solution, have my 5.

CPallini · Answer 2 · 2019-05-15T04:53:00

Solution 2

You may also pass an array of struct to your InitEvents function, something like (but more robust)

C

typedef struct
{
  HANDLE handle;
  char * name;
} Event;


void InitEvents(Event event[], size_t event_count)
{ 
  event[0].handle = ...
  event[0].name = ...
  
  event[1].handle = ...
  event[1].name = ...
}

int main()
{

  Event event[2];


  InitEvents(event);

  //...
}

Posted 15-May-19 4:53am

CPallini

Comments

KarstenK 15-May-19 11:44am

I would suggest a global struct, so it is visible in the whole code without fizzling.

CPallini 15-May-19 13:40pm

Trust me, globals are bad.