CODEWITHSUNDEEP
cwindowsmemory-management
tguclu
tguclu

Reputation: 719

Displaying the amount of memory allocated

Hi I'm writing some test stuff to see the amount of memory that allocated displayed correctly

in Windows TasK manager. Below is the code;

int main(int argc,char* argv[])
{
 struct stat st;
 char commandXCopy[200];
 char commandDelete[200];

 char *fNames[2^16];
 int i =0;
    char *ptr = (char *)malloc(sizeof(char) * 2^32);
     printf("\nTEST");

    if(!ptr)
            printf("\nCan not allocate");
    else
            printf("\nMemory allocate");


     while(1==1)
     {
     };

I try to make huge allocations from stack and heap. But all I see on task manager->processes is ~800K.

And I don't see "Can not allocate" message either.

I have Windows 32bit XP Pro and use gcc and application is a dos application.

gcc test.c

Regards

Upvotes: 1

Views: 136

Answers (1)

paxdiablo
paxdiablo

Reputation: 881503

I think you may be suffering under a misapprehension: 2^32 is not 232 (4G, assuming your bytes are eight bits long, which I will for the purposes of this answer) in C.

^ is the bitwise XOR operator. So what you're actually allocating is:

     binary        hex     decimal
    ---------      ----    -------
    0010 0000      0x20      32
xor 0000 0010      0x02       2
    =========
    0010 0010      0x22      34

or 34 bytes. Similarly, 2^31 would give you 29 bytes so what you may think should be a 2G difference (232 - 231) is really only 5 bytes.

If you want to do powers in C, you should look at the pow() function but I doubt you'll be able to get 4G of memory (perhaps on a 64-bit OS but even then, that's an awful lot).

And just one other thing: sizeof(char) is always 1 - there's no need to multiply by it.

Upvotes: 5

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