Unable to retrieve process memory usage Delphi - delphi

Question

I am trying to write a little utility to retrieve a list of running processes on a computer and the memory being used by each process.
So far I have the following Delphi code:
{ ******************************************************************
Return list of running processes
******************************************************************* }
procedure TGkrTools.GetProcList(var thelist : tstrings);
var
ExeName : string;
PSize : cardinal;
PID : cardinal;
TheLoop : boolean;
proc : PROCESSENTRY32;
hSnap : HWND;
pmc : PPROCESS_MEMORY_COUNTERS;
cb : integer;
begin
thelist.Clear; // Clear the list on entry
proc.dwSize := SizeOf(PROCESSENTRY32);//Give proc.dwSize the Size of bytes of PROCESSENTRY32
hSnap := CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
TheLoop := Process32First(hSnap,proc);
while Integer(TheLoop) <> 0 do
begin
ExeName := ExtractFileName(proc.szExeFile); // Name of process executable
cb := SizeOf(_PROCESS_MEMORY_COUNTERS);
GetMem(pmc, cb);
pmc^.cb := cb;
PID:=proc.th32ProcessID;
if GetProcessMemoryInfo(PID, pmc, cb) then
begin
Psize:=pmc^.WorkingSetSize;
end
else
begin
Psize:=0;
end;
Thelist.Add(ExeName + ' ' + IntToStr(Psize)+ ' ' + IntToStr(PID));
TheLoop := Process32Next(hSnap,proc);//Looper is oposite Zero until there is a program to process by this function
end;
end;
I successfully retrieve the "ExeName" and "PID" but when I execute the GetProcessMemoryInfo function, the call returns "false".
Any ideas on what is wrong in my code?
I'm running this on a 32 bit Windows 7 machine.
Thanks in advance,
Gudfinnur Kristjansson

Answer 1

You should read the documentation carefully. The first parameter is a process handle rather than a process ID. You need to call OpenProcess to get a process handle from the process ID. The documentation also says:
The handle must have the PROCESS_QUERY_INFORMATION or PROCESS_QUERY_LIMITED_INFORMATION access right and the PROCESS_VM_READ access right.
Make sure that you request those access rights when calling OpenProcess.
When you are done with the handle, close it with CloseHandle. Again, read the documentation closely.
Do note that your current code leaks the dynamic memory that you allocate. There is actually no need to allocate memory dynamically. Rather than declaring a PPROCESS_MEMORY_COUNTERS, pointer to the struct, declare a variable of type PPROCESS_MEMORY_COUNTERS. Then the memory can be allocated automatically on the stack.
One final point to make is that the documentation also tells you to call GetLastError if the function fails. Do make sure that you do this to try to diagnose any failures.