Thread: Structures , Callback Functions , LibCurl - Need Some Help!

printf("%s",MemBlock->Data[0]);So Playing Around with structures :

Code:

#include <stdio.h>
#include <stdlib.h>


struct MemoryBlock
{
    char *Data;
    size_t Size; //size_t is a unsigned integer
};


int LoadFromFile(char *FileName,void *GenericPointer)
{
    FILE *Source;
    size_t Size = 0;
    Source = fopen(FileName,"r");
    struct MemoryBlock *MemBlock;
    MemBlock = GenericPointer;
    if (Source!=NULL)
    {
        char ch;
        while((ch = fgetc(Source))!=EOF)
        {
        Size++;
        MemBlock->Data=MemBlock->Data+ch; //Fills my structure with data
        };
        MemBlock->Size=Size;
    }
    return 1; //This line will only be reached if the file could not be found.
}
int PrintMemBlock(void *GenericPointer)
{
struct MemoryBlock *MemBlock;
MemBlock=GenericPointer;
printf("%s\n","Memory Block:");
printf("\nSize :%i\n",MemBlock->Size);


printf("%s",MemBlock->Data[0]);
return 0;
}


int main()
{
    struct MemoryBlock MemBlock;
    MemBlock.Size = 3;
    MemBlock.Data="a";
    LoadFromFile("BlobFile.txt",&MemBlock);
    PrintMemBlock(&MemBlock);
    return 0;
}

This is bugging me - printf("%s",MemBlock->Data[0]);
1. ) How do I work with the first element of the Data variable?


On to callback functions :

Code:

#include <stdio.h>
#include <stdlib.h>


struct Rectangle
{
   int Width,Length;
   float Area;
   char *Name;
};


void Construct_Rectangle(struct Rectangle *StructPnt,char *AName,int ALength,int AWidth)
{
    StructPnt->Name = AName; //-> is basically just dereferancing the struct like &StructPnt....
    StructPnt->Width = AWidth;
    StructPnt->Length = ALength;
    StructPnt->Area = AWidth * ALength;
}


void Print_Rectangle(struct Rectangle *StructPnt)
{
    printf("Name : %s\n",StructPnt->Name);
    printf("Width : %i\n",StructPnt->Width);
    printf("Length : %i\n",StructPnt->Length);
    printf("Area : %f\n",StructPnt->Area);


}


void Count(void(*Referance)())
{
    int i = 1 ;
    for(i;i!=10;i++)
    {
        printf("%i\n",i);
        Referance(i);
    }
}
void CallBack(int a)
{
    if (a%2==0) printf("%s\n","Called A");
        else printf("%s\n","Called B");
}




int main()
{
    //Void pointer
    int AString = 5;
    void *Pntr; //Generic Pointer
    Pntr = AString;
    printf("%i\n",Pntr);
    //Structures
    struct Rectangle Test;
    Construct_Rectangle(&Test,"Bobby",5,10);
    Print_Rectangle(&Test);
    Count(CallBack);
    return 0;


    //Callbacks


}

Just any help with this , if I'm going wrong somewhere. General Tips!

And then libcurl :O

Code:

#include <stdio.h>
#include <stdlib.h>
#include <include/curl/curl.h>
#include <include/curl/easy.h> //#includes are funny because i had no idea what i was doing setting up curl


static int CBFWrite(void *Contents,size_t Size,size_t NumberOfUnits,void *UserPnter);
typedef struct Memblock_t;
struct Memblock_t
{
    char *Data;
    size_t Size;
};




static int CBFWrite(void *Contents,size_t Size,size_t NumberOfUnits,void *UserPnter)
//Callback structure  : Void Pointer , size_t , size_t , void Pointer
{
    size_t RawSize = Size * NumberOfUnits;
    struct MemBlock_t *Chunk;
    Chunk = (struct Memblock_t *)UserPnter;


    return 0;
}






int main()
{
    CURL *CurlHandle;
    CURLcode CurlResult;
    CurlHandle = curl_easy_init();
    struct MemBlock_t DataChunk;


    curl_easy_setopt(CurlHandle,CURLOPT_URL,"http://www.youtube.com");
    curl_easy_setopt(CurlHandle,CURLOPT_WRITEFUNCTION,CBFWrite);
    curl_easy_setopt(CurlHandle,CURLOPT_WRITEDATA,(void *)&DataChunk);


    CurlResult = curl_easy_perform(CurlHandle);
    if (CurlResult == CURLE_OK)
    {
        printf("%s\n","Executed With No Errors");
    }
    else
    {
        printf("%s\n","Error");
    }




    curl_global_cleanup();
    return 0;
}

I get an error on this line
Chunk = (struct Memblock_t *)UserPnter;
Error : dereferencing pointer to incomplete type


Aaaaaaand this line
struct MemBlock_t DataChunk;
Error : Size of datachunk is unknown.



As I understand it instead of pushing everything to the stdout by using curl_easy_opt(...CURLOPT_WRITEFUNCTION,CallbackFun ction)
curl will now send it's output to that particular function.

Now this

Code:

 static int CBFWrite(void *Contents,size_t Size,size_t NumberOfUnits,void *UserPnter)

is the function Curl is expecting ; That being said if I were to lets say remove a parameter - would my program simply output garbash or just skip that variable (like if what curl is expecting in the callback function was set up in a parallel array ) Eg:

My main function expects int a , char b , int c
but my callback function only provides int a and char b
what happens to int c?

As of now i feel the structures and callback functions are much more important than learning to use libcurl. Please help!

Saw Someting else:

I guess this comes from delphi XD
MemBlock->Data=MemBlock->Data+ch; //Fills my structure with data
Why does this line work? Isnt it the same to lets say AString = AString + 'c'
Which again in delphi is fine but in c shouldnt i use strcat()
Also. Shouldnt i be allocating memory somewhere . im confused.

Let's look at your first example with corrections.

Code:

#include <stdio.h>
#include <stdlib.h>

struct MemoryBlock
{
    char *Data;
    size_t Size; //size_t is a unsigned integer
};

int LoadFromFile(char *FileName,void *GenericPointer)
{
    FILE *Source;
    size_t Size = 0;
    Source = fopen(FileName,"r");
    struct MemoryBlock *MemBlock;
    MemBlock = GenericPointer;
    if (Source!=NULL)
    {
        int ch;
        //!! read the file, while there is space to store the result
        while( Size < MemBlock->Size &&
              (ch = fgetc(Source))!=EOF)
        {
            //!! this actually appends to a buffer
            MemBlock->Data[Size++] = ch;
        }
        //!! update the max size, with the actual amount used.
        MemBlock->Size=Size;
        fclose(Source);
    }
    return 1;
}

int PrintMemBlock(void *GenericPointer)
{
  struct MemoryBlock *MemBlock;
  MemBlock=GenericPointer;
  printf("%s\n","Memory Block:");
  printf("\nSize :%zd\n",MemBlock->Size);
  //!! restrict printing to only the valid length
  printf("%*s",(int)MemBlock->Size,MemBlock->Data);
  return 0;
}


int main()
{
    struct MemoryBlock MemBlock;
    MemBlock.Size = 50;
    MemBlock.Data = malloc(50); //!! Make it point at usable memory, for the size needed
    LoadFromFile("bar.c",&MemBlock);
    PrintMemBlock(&MemBlock);
    return 0;
}

Now you could adopt the convention that if .Size is 0 and .Data is NULL, then LoadFromFile() should call malloc/realloc itself until either memory is exhausted or the whole file has been read. Either approach is fine.

As for your curl program,
> struct Memblock_t
...
> struct MemBlock_t *Chunk;
C is case sensitive.