Thread: pointer exception???

Hi
I tried malloc a big chunk of memory and use one pointer and tried with a secondary
buffer2=buffer+numberofelement;
*buffer2 = result;
I got a pointer exception inside this loop,despite I have malloc several megabytes
so I went back what I am used to,declare a huge buffer[] and use buffer[numberofelement]
but I want to learn to get dynamic allocation right

Show some code.

Did you forget to multiply by sizeof(type) when you called malloc?

Originally Posted by Salem

Show some code.

Did you forget to multiply by sizeof(type) when you called malloc?

Realize problem is allocate 20000000000 ints are too much,its not bytes
Need to add IF to check malloc fails
Pointer math needs to use unsigned ints only?

Originally Posted by I C everything

Pointer math needs to use unsigned ints only?

No, you can use negative integers, e.g., to traverse an array in reverse, but you should keep in mind that the valid pointers are those that point to the first element to one past the last element inclusive, and that you may only dereference valid pointers except the one past the end pointer.

thanks laserlight,probably good if you code that way if its on purpose

ok I post my messy looking code so far,with working code with buffer3 and with not working is buffer and buffer2,
first need to figure out to make it work,try floats later

Code:

#include "pch.h"
#include <iostream>
using namespace std;
int maxram;
int *buffer;
int *buffer2;
int buffer3[1024*1048];
float a, b, c, d, e, f, g, h;
float r, r2, r3, r4;
int i, j, k, l,composite;


int main()
{
    maxram = 0x2000000000;
    buffer=(int*)malloc(maxram);
    memset(buffer, -1, maxram);
    


    cout << "Primes and composites !\n";
     
    for (i = 0; i < 1024000; i++) { buffer3[i] = 0;
    }
    
    for (i = 2; i < 1023;i=i+1 ) {
        for (j = 2; j < 1023; j=j+1) {
            composite = i * j;
            buffer2 = buffer + composite;
            buffer3[composite] = composite;
            //*buffer2 = composite;
        }
    }
    cout << "composites and primes:";
    
        for (k = 2; k < 121; k=k+1) {
            i = buffer3[k];
            j = k;
            if (i == 0) { 
                cout << "            prime " << j << "\n";
            }
            else cout << "composite " << i << "\n";
        }
    
    free(buffer);
    system("PAUSE");


}

121 in the last loop is on purpose temporary easier to check smaller printout
I have tried with optimizations in i,j forloop to step thru all odd numbers,but that breaks code so it prints lots of nonprimes as primes

Originally Posted by Click_here

That is C++ and you are on the C forum

is that why IDE shows malloc,free,system,memset in pink,those are C code,C++ uses new,create,delete?

Can I access mellowed memory just like I want?
For example mix handle 32bit sized pixels,it's,with unsigned chars when handle a color channel separately,for example blue in argb format?

Or long long 64 bitcombined with 32 bit into?

yes,sorry,wrote it on a device with autocorrect
does this mean I need to have one *int,one *char, one *long pointer to the same buffer,sometimes I copy whole buffer,sometimes I want to move 32bit pixels,sometimes I want to manipulate channels,for example light up rgb or blend together
I more understand really lowlevel pointers,rusty when it comes to C/C++