Question

I think this is a trivial question, but I am never able to get this to work!

I have made a function call through a function pointer inside a .lib and attached the .lib to an application program which sets the function pointer, outside the library. The following is the code snippet

Lib :

void (*PopulateBuffer)(byte *NALBuffer,unsigned int *readbytes); // The Declaration

PopulateBuffer(NALBuffer,&readbytes); // The function Call

Application :

extern void (*PopulateBuffer)(char *NALBuffer,unsigned int *readbytes);


void UpdateNALBuff(char *Buffer,unsigned int *readbytes)

{

    //Buffer content is updated
    //readbytes is updated

}

main()

{

    PopulateBuffer= &UpdateNALBuff;

        LibMain(); // this is the main call in which the function pointer is called
}

Am I doing this right???
Cause when ever the function call approaches in the library, it throws me the following error :

Unhandled exception at 0x00536e88 in DecoderTestApp.exe: 0xC0000005: Access violation reading location 0x7ffef045.

Answer 1

Generally for dealing with function pointers, you do it in the following way:

typedef void (*PopulateBuffer)(byte *NALBuffer,unsigned int *readbytes); //This should be exposed from the library

Create a pointer variable inside the library for storing the function pointer

PopulateBuffer PpBuffFunc = NULL;

Provide a function from the library to set the function

void setPopulateBufferFuncPointer(PopulateBuffer func)
{
    PpBuffFunc = func;
}

Now call this function from your application

setPopulateBufferFuncPointer(UpdateNALBuff);

Inside the lib at appropriate place, call the PpBuffFunc by passing appropriate parameters