Platform SDK: Memory

GlobalMemoryStatus

The GlobalMemoryStatus function obtains information about the system's current usage of both physical and virtual memory.

To obtain information about the extended portion of the virtual address space, or if your application may run on computers with more than 4 GB of main memory, use the GlobalMemoryStatusEx function.

VOID GlobalMemoryStatus(
  LPMEMORYSTATUS lpBuffer   // memory status structure
);

Parameters

lpBuffer: [out] Pointer to a MEMORYSTATUS structure. The GlobalMemoryStatus function stores information about current memory availability into this structure.

Return Values

This function does not return a value.

Remarks

You can use the GlobalMemoryStatus function to determine how much memory your application can allocate without severely impacting other applications.

The information returned by the GlobalMemoryStatus function is volatile. There is no guarantee that two sequential calls to this function will return the same information.

On computers with more than 4 GB of memory, the GlobalMemoryStatus function can return incorrect information. Windows 2000 reports a value of -1 to indicate an overflow. Earlier versions of Windows NT report a value that is the real amount of memory, modulo 4 GB. For this reason, on Windows 2000, use the GlobalMemoryStatusEx function instead.

On Intel x86 computers with more than 2 GB and less than 4 GB of memory, the GlobalMemoryStatus function will always return 2 GB in the dwTotalPhys member of the MEMORYSTATUS structure. Similarly, if the total available memory is between 2 and 4 GB, the dwAvailPhys member of the MEMORYSTATUS structure will be rounded down to 2 GB. If the executable is linked using the /LARGEADDRESSWARE linker option, then the GlobalMemoryStatus function will return the correct amount of physical memory in both members.

Example

The program following shows a simple use of the GlobalMemoryStatus function.

//  Sample output:
//  c:\>global
//  The MemoryStatus structure is 32 bytes long.
//  It should be 32.
//  78 percent of memory is in use.
//  There are   65076 total Kbytes of physical memory.
//  There are   13756 free Kbytes of physical memory.
//  There are  150960 total Kbytes of paging file.
//  There are   87816 free Kbytes of paging file.
//  There are  1fff80 total Kbytes of virtual memory.
//  There are  1fe770 free Kbytes of virtual memory.

#include <windows.h>

// Use to change the divisor from Kb to Mb.

#define DIV 1024
// #define DIV 1

char *divisor = "K";
// char *divisor = "";

// Handle the width of the field in which to print numbers this way to
// make changes easier. The asterisk in the print format specifier
// "%*ld" takes an int from the argument list, and uses it to pad and
// right-justify the number being formatted.
#define WIDTH 7

void main(int argc, char *argv[])
{
  MEMORYSTATUS stat;

  GlobalMemoryStatus (&stat);

  printf ("The MemoryStatus structure is %ld bytes long.\n",
          stat.dwLength);
  printf ("It should be %d.\n", sizeof (stat));
  printf ("%ld percent of memory is in use.\n",
          stat.dwMemoryLoad);
  printf ("There are %*ld total %sbytes of physical memory.\n",
          WIDTH, stat.dwTotalPhys/DIV, divisor);
  printf ("There are %*ld free %sbytes of physical memory.\n",
          WIDTH, stat.dwAvailPhys/DIV, divisor);
  printf ("There are %*ld total %sbytes of paging file.\n",
          WIDTH, stat.dwTotalPageFile/DIV, divisor);
  printf ("There are %*ld free %sbytes of paging file.\n",
          WIDTH, stat.dwAvailPageFile/DIV, divisor);
  printf ("There are %*lx total %sbytes of virtual memory.\n",
          WIDTH, stat.dwTotalVirtual/DIV, divisor);
  printf ("There are %*lx free %sbytes of virtual memory.\n",
          WIDTH, stat.dwAvailVirtual/DIV, divisor);
}

Requirements