Segmentation fault: 11 in c program (dynamic memory allocation)

Question

I have the following piece of code which allocates some memory.

Some used initialisations:

#define MEM_POOL_SIZE 600

typedef struct {
size size;
mem_status status;
} mem_chunk_header;

unsigned char* ptr;

When I call this function as follows

ma_malloc(600)

it should return NULL. But I get a segmentation fault: 11. I tried using GDB, but then I run into different problems...

void* ma_malloc(size tsize)
{
    mem_chunk_header header;

    unsigned char* searchPtr = ptr;
    int oldSize = 0;
    int stop = 0;

    while(((searchPtr-ptr)/sizeof(unsigned char) < MEM_POOL_SIZE) && (stop >= 0))
    {
            if((*searchPtr = 0xFF) && ((getSize(searchPtr) >= (tsize))))
            {
                    stop = -1;
            }
            else
            {
                    if(getSize(searchPtr) == 0)
                    {
                            return NULL;
                    }
                    else
                    {
                            searchPtr += (getSize(searchPtr)+header.size);
                    }
            }
    }
    if(stop == 0)
    {
            printf("%s\n","No free space available");
            return NULL;
    }
    else
    {
            oldSize = getSize(searchPtr);
            //Update header
            *searchPtr = 0xAA;
            *(searchPtr+1) = (unsigned char) ((tsize)/256);
            *(searchPtr+2) = (unsigned char) ((tsize)%256);
            //Update footer
            updateFooter(searchPtr);
            //New overhead
            unsigned char* newPtr = (searchPtr+(getSize(searchPtr))+header.size);
            unsigned char* nextPtr = (unsigned char*) (searchPtr+oldSize+header.size);
            int leftoverSize = ((nextPtr-newPtr)/sizeof(unsigned char));

            if(leftoverSize == 0)
            {
                    //Do nothing
            }
            else
            if(leftoverSize <= header.size)
            {
                    unsigned int tempSize = getSize(searchPtr) + leftoverSize;
                    //Update header
                    *(searchPtr+1) = (unsigned char) (tempSize/256);
                    *(searchPtr+2) = (tempSize%256);
                    //footer
                    updateFooter(searchPtr);
            }
    else
            {
                    //Update header
                    *newPtr = 0xFF;
                    *(newPtr+1) = (unsigned char) ((leftoverSize-header.size)/256);
                    *(newPtr+2) = (unsigned char) ((leftoverSize-header.size)%256);
                    //Update footer
                    updateFooter(newPtr);
            }
    }
    return searchPtr;
}

I've been looking at this for a while now, but I can't see why it is giving me this error.

`ptr` is declared at the global level, but you don't show assigning it to anything. Your code shows `searchPtr` being assigned to it, and dereferenced, which would cause a fault. Is ptr actually assigned to memory somewhere in code you've not shown? — brycem, Apr 08 '16 at 14:06
What is `getSize`? And yeah you haven't initialized any of your variables, so your program will therefore halt and catch fire, if you are lucky. Overall, try to simplify this function by splitting it in several. — Lundin, Apr 08 '16 at 14:07
_I tried using GDB, but then I run into different problems..._ could be intersting to know what kind off "different" problems these are. — Jabberwocky, Apr 08 '16 at 14:10
Is `(*searchPtr = 0xFF)` in the `if` statement intended to be an assignment? I don't think so.. — Eugene Sh., Apr 08 '16 at 14:13
@MichaelWalz not really important, not correctly installed (I assume) — Yannick Maris, Apr 08 '16 at 14:19
A little? Hehe... Such a mistakes caused spaceships to crash. — Eugene Sh., Apr 08 '16 at 14:21
Possible duplicate of [Definitive List of Common Reasons for Segmentation Faults](http://stackoverflow.com/questions/33047452/definitive-list-of-common-reasons-for-segmentation-faults) — CodeMouse92, Apr 10 '16 at 00:38

Segmentation fault: 11 in c program (dynamic memory allocation)

0 Answers0