Allocate memory for huge node tree dynamically

Question

I'm trying to make a function that allocates memory in blocks and than is able to assign a memory pointer for different structures linked together.

#define MEMSIZE 50*1024*1024*sizeof(char)
#include "globals.h"
void *AddBlock(void){
    memstart = (char*) calloc(1,MEMSIZE);
    if(memstart==NULL){
        printf("Hittade inte minne...:\n");
        getchar();
        throw 1;
    }
    memptr = memstart;
    return memstart;
}

void* GetSpace(size_t size){ //gör nytt block eller putta fram pekaren
                             //makes a new block or increases ptr

    void *tmp = NULL;//where the data should be stored
    if(( memptr+size+1 >= memstart+MEMSIZE) )
        tmp = AddBlock();
    else
    {
        tmp = memptr;
        memptr+=size;
    }
    return tmp;
}

void InitMem(void){ //init of memory globals
    AddBlock();
}

memptr and memstart are extern char*. memstart is start of block and memptr is where you are at. InitMem is run in main upon start.

globals .h

extern char *memstart;
extern char *memptr;

globals .cpp

char *memstart;
char *memptr;

E.g. struct Node* TheNode = GetSpace(sizeof(struct Node));

But the code works really bad and gives a lot of glitches in the program.

Is there any common way to do this? When I allocate memory for each structure with malloc there are way to much overhead and that's a huge deal since the tree consists of millions of nodes.

Answer 1

This leg of code has a problem

if(( memptr+size+1 >= memstart+MEMSIZE) )
    tmp = AddBlock();

because it is not advancing memptr by size.