How to Get Memory Usage Under Windows in C++

How to get memory usage under Windows in C++

A good starting point would be GetProcessMemoryInfo, which reports various memory info about the specified process. You can pass GetCurrentProcess() as the process handle in order to get information about the calling process.

Probably the WorkingSetSize member of PROCESS_MEMORY_COUNTERS is the closest match to the Mem Usage coulmn in task manager, but it's not going to be exactly the same. I would experiment with the different values to find the one that's closest to your needs.

C++: Measuring memory usage from within the program, Windows and Linux

To know how much physical memory your process takes you need to query the process working set or, more likely, the private working set. The working set is (more or less) the amount of physical pages in RAM your process uses. Private working set excludes shared memory.

See

• What is private bytes, virtual bytes, working set?
• How to interpret Windows Task Manager?
• https://blogs.msdn.microsoft.com/tims/2010/10/29/pdc10-mysteries-of-windows-memory-management-revealed-part-two/

for terminology and a little bit more details.

There are performance counters for both metrics.

(You can also use QueryWorkingSet(Ex) and calculate that on your own, but that's just nasty in my opinion. You can get the (non-private) working set with GetProcessMemoryInfo.)

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But the more interesting question is whether or not this helps your program to make useful decisions. If nobody's asking for memory or using it, the mere fact that you're using most of the physical memory is of no interest. Or are you worried about your program alone using too much memory?

You haven't said anything about the algorithms it employs or its memory usage patterns. If it uses lots of memory, but does this mostly sequentially, and comes back to old memory relatively rarely it might not be a problem. Windows writes "old" pages to disk eagerly, before paging out resident pages is completely necessary to supply demand for physical memory. If everything goes well, reusing these already written to disk pages for something else is really cheap.

If your real concern is memory thrashing ("virtual memory will be of no use due to swapping overhead"), then this is what you should be looking for, rather than trying to infer (or guess...) that from the amount of physical memory used. A more useful metric would be page faults per unit of time. It just so happens that there are performance counters for this too. See, for example Evaluating Memory and Cache Usage.

I suspect this to be a better metric to base your decision on.

How to get the total 'percentage' of RAM in C++?

You need to call GlobalMemoryStatusEx to get the data.

MEMORYSTATUSEX statex;
statex.dwLength = sizeof (statex);
GlobalMemoryStatusEx (&statex);

// it already contains the percentage
auto memory_load = statex.dwMemoryLoad; 

// or calculate it from other field if need more digits.
auto memory_load = 1 - (double)statex.ullAvailPhys / statex.ullTotalPhys;

note: you should check the return value of GlobalMemoryStatusEx in case it fail.

How to get available memory C++/g++?

Having read through these answers I'm astonished that so many take the stance that OP's computer memory belongs to others. It's his computer and his memory to do with as he sees fit, even if it breaks other systems taking a claim it. It's an interesting question. On a more primitive system I had memavail() which would tell me this. Why shouldn't the OP take as much memory as he wants without upsetting other systems?

Here's a solution that allocates less than half the memory available, just to be kind. Output was:

Required FFFFFFFF

Required 7FFFFFFF

Required 3FFFFFFF

Memory size allocated = 1FFFFFFF

#include <stdio.h>
#include <stdlib.h>

#define MINREQ      0xFFF   // arbitrary minimum

int main(void)
{
    unsigned int required = (unsigned int)-1; // adapt to native uint
    char *mem = NULL; 
    while (mem == NULL) {
        printf ("Required %X\n", required);
        mem = malloc (required);
        if ((required >>= 1) < MINREQ) {
            if (mem) free (mem);
            printf ("Cannot allocate enough memory\n");
            return (1);
        }
    }

    free (mem);
    mem = malloc (required);
    if (mem == NULL) {
        printf ("Cannot enough allocate memory\n");
        return (1);
    }
    printf ("Memory size allocated = %X\n", required);
    free (mem);
    return 0;
}

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