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digitalmars.D.learn - Error while trying to allocate memory (malloc)

reply "CrudOMatic" <crudomatic gmail.com> writes:
The following code:

import std.stdio, std.cstream, std.c.stdlib;

private {
	//import rescache.cache;
	//import mm.mempool;
}

void main(string[] args)
{
	// press <Return> before program begins
	din.getc();
	
	memoryPool memPool = new memoryPool(1024);
	writeln("Block Allocated!");
	
	// press <Return> to end program
	din.getc();
	//return cast(int)0;
}

	// Growable/shrinkable memory pool, for speedy memory allocation
	class memoryPool {
		private:
			// Allocation header, count and keep track of allocs and keep 
first, last info
			struct s_allocHeader {
				int m_allocCount; // count number of allocations from pool
				s_allocInfo* p_first; // pointer to first allocation info 
struct
				s_allocInfo* p_last; // pointer to last alloc info struct 
(should be null if only one)
			}
			// Keep track of allocations from the memory pool
			struct s_allocInfo {
				align(4) // align on 4-byte boundaries
				void* p_data; // pointer to data chunk allocated out
				void* p_inBlock; // pointer to block this allocation was made 
in
				int m_dataSize; // size of allocated chunk
				s_allocInfo* p_next; // pointer to next allocation list entry
			}
			
			// Block header, count and keep track of system allocs and 
keep first, last info
			struct s_blockHeader {
				int m_blockCount; // count number of allocations from system
				s_blockInfo* p_first; // pointer to first block info struct
				s_blockInfo* p_last; // pointer to last block info struct 
(should be null if only one)
			}
			// Keep track of block allocations
			struct s_blockInfo {
				align(4) // align on 4-byte boundaries
				void* p_block; // pointer to the memory allocated from the 
system
				int m_blockSize; // size of block allocated from the system
				bool m_poolMember; // whether or not the block was allocated 
for the memory pool
				s_blockInfo* p_next; // pointer to next block list entry
			}
			
			int m_CHUNK_SIZE = 128; // n-byte allocations from the pool
			int m_BLOCK_SIZE = 4096; // pool block size
		
		public:	
			// Allocator
			//void* alloc(int numChunks = 1, bool useMemPool = true) { }
			// Deallocator
			void free() { }
			// Grow the memory pool
			void growPool(int numBlocks = 1) { }
			// Shrink the memory pool
			void shrinkPool(int numBlocks = 1) { }
			
			// Constructor; pass it the initial memory pool size in MB
			this(int initialPoolSize) {
				// set up allocation list
				s_allocHeader* m_allocList;
				// set up block list
				s_blockHeader* m_blockList;
				
				// create initial block info reference, and set block count 
to 1
				m_blockList.p_first = malloc(s_blockInfo.sizeof);
				//m_blockList.m_blockCount = 1;
				// allocate initial block of memory and store it in block 
info reference
				//s_blockInfo* tmp = m_blockList.p_first;
				//tmp.p_block = malloc(cast(size_t)initialPoolSize);
				//tmp.m_blockSize = initialPoolSize;
				//tmp.m_poolMember = true;
				//tmp.p_next = null;
			}
			// Deconstructor
			~this() { }
	} // END of c_memoryPool class

when compiled, gives the error:

Error: cannot implicitly convert expression (malloc(16u)) of type 
void* to s_blockInfo*

on line (75):

m_blockList.p_first = malloc(s_blockInfo.sizeof);

What is going on here?

I even tried using new, but got an Access Violation

Any help would be appreciated.
Aug 06 2012
next sibling parent "Minas Mina" <minas_mina1990 hotmail.co.uk> writes:
Maybe you need a cast before malloc to convert it to a 
"s_blockInfo*"?
Aug 06 2012
prev sibling next sibling parent "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:

 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?



Just did, and compiled. Errored out with (from my IDE):

 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...



Running it directly gives me:

object.Error: Access Violation
----------------
I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D 
main
----------------
Aug 06 2012
prev sibling next sibling parent "Eyyub" <eyyub.pangearaion gmail.com> writes:
On Monday, 6 August 2012 at 13:59:35 UTC, CrudOMatic wrote:

 On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:

 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?



 Just did, and compiled. Errored out with (from my IDE):

 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...



 Running it directly gives me:

 object.Error: Access Violation
 ----------------
 I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D 
 main
 ----------------



You get an Access Violation error because `m_blockList` is null.
Aug 06 2012
prev sibling next sibling parent "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 14:14:12 UTC, Eyyub wrote:

 On Monday, 6 August 2012 at 13:59:35 UTC, CrudOMatic wrote:

 On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:

 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?



 Just did, and compiled. Errored out with (from my IDE):

 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...



 Running it directly gives me:

 object.Error: Access Violation
 ----------------
 I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D 
 main
 ----------------



 You get an Access Violation error because `m_blockList` is null.



So, do I use new or what? In C it was just declare and go...
Aug 06 2012
prev sibling next sibling parent "Eyyub" <eyyub.pangearaion gmail.com> writes:
On Monday, 6 August 2012 at 14:55:05 UTC, CrudOMatic wrote:

 In C it was just declare and go...



Really ? I don't think, because : s_blockHeader* m_blockList;
Here, m_blockList is a pointer to s_blockHeader struct, and so 
the default value is `null`.
So, trying to access to(?) a struct member whereas the pointer is 
set to null, is a nonsense.
Tell me if I'm wrong. (I did not programming in C since 2 years)


 So, do I use new or what?



you can use `new` or `malloc`.(it depends on what you need)

May be someone can help you better than me.
Aug 06 2012
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:

 Tell me if I'm wrong. (I did not programming in C since 2 years)



You're not wrong. m_blockList is a pointer and OP needs to allocate an
s_blockHeader instance before he uses it:

s_blockHeader* m_blockList = cast(s_blockHeader*)malloc(s_blockHeader.sizeof);
Aug 06 2012
prev sibling next sibling parent "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 15:36:03 UTC, Andrej Mitrovic wrote:

 On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:

 Tell me if I'm wrong. (I did not programming in C since 2 
 years)



 You're not wrong. m_blockList is a pointer and OP needs to 
 allocate an
 s_blockHeader instance before he uses it:

 s_blockHeader* m_blockList = 
 cast(s_blockHeader*)malloc(s_blockHeader.sizeof);



oops. Thanks. brainfart I guess, been a while since I've used any 
C like languages.
Aug 06 2012
prev sibling next sibling parent "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 15:36:03 UTC, Andrej Mitrovic wrote:

 On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:

 Tell me if I'm wrong. (I did not programming in C since 2 
 years)



 You're not wrong. m_blockList is a pointer and OP needs to 
 allocate an
 s_blockHeader instance before he uses it:

 s_blockHeader* m_blockList = 
 cast(s_blockHeader*)malloc(s_blockHeader.sizeof);



another quick question - are these allocations automatically 
entered into the GC heap? If so then I can just disable garbage 
collection?
Aug 06 2012
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/6/12, CrudOMatic <crudomatic gmail.com> wrote:

 another quick question - are these allocations automatically
 entered into the GC heap? If so then I can just disable garbage
 collection?



No, there is the standard C malloc/free in std.c.stdlib which you're
using, and then there's the GC.malloc and GC.free in core.memory if
you want to allocate from the GC heap.
Aug 06 2012
prev sibling parent Marco Leise <Marco.Leise gmx.de> writes:
Am Mon, 6 Aug 2012 18:25:01 +0200
schrieb Andrej Mitrovic <andrej.mitrovich gmail.com>:


 On 8/6/12, CrudOMatic <crudomatic gmail.com> wrote:

 another quick question - are these allocations automatically
 entered into the GC heap? If so then I can just disable garbage
 collection?



 No, there is the standard C malloc/free in std.c.stdlib which you're
 using, and then there's the GC.malloc and GC.free in core.memory if
 you want to allocate from the GC heap.



And in the latter case write: 
auto m_blockList = new s_blockHeader;

-- 
Marco
Aug 07 2012