GetProcessId doesn't find any process - c++

Question

I'm using the following code to try to get the PID of notepad.exe, but it doesn't find the process.
I'm currently running on Windows 10 and compiling using VS Studio 19 as Release x64.
Also tried to find other processes, like chrome.exe, calculator.exe, etc, but couldn't find anything.
DWORD GetProcessId(LPCTSTR ProcessName)
{
PROCESSENTRY32 pt;
HANDLE hsnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
std::wcout << "Error: " << GetLastError() << std::endl; // Error: 0
pt.dwSize = sizeof(PROCESSENTRY32);
std::wcout << "Error: " << GetLastError() << std::endl; // Error: 0
if (Process32First(hsnap, &pt)) { // must call this first
do {
if (!lstrcmpi(pt.szExeFile, ProcessName)) {
CloseHandle(hsnap);
return pt.th32ProcessID;
}
} while (Process32Next(hsnap, &pt));
}
std::wcout << "Error: " << GetLastError() << std::endl; // Error: 24
CloseHandle(hsnap); // close handle on failure
return 0;
}
int _tmain(int argc, _TCHAR* argv[])
{
DWORD processId;
processId = GetProcessId(TEXT("notepad.exe"));
std::wcout << "processId: " << processId << std::endl;
return 0;
}
While debugging, I see the code is skipping the do while and jumping directly to CloseHandle(hsnap)
GetLastError() returns 24 at this line.

Answer 1

The image you posted of your debug output window shows pt.dwSize is set to 2168. This looks wrong. pt.dwSize is important, it used by Windows for version control.
On my computer sizeof(PROCESSENTRY32) is 556 (it depends on Windows version, I am using Windows 10). If project is not Unicode, the size should about half that. In VS, you can right click on PROCESSENTRY32 and it takes you to this definition:
typedef struct tagPROCESSENTRY32W
{
DWORD dwSize;
DWORD cntUsage;
DWORD th32ProcessID; // this process
ULONG_PTR th32DefaultHeapID;
DWORD th32ModuleID; // associated exe
DWORD cntThreads;
DWORD th32ParentProcessID; // this process's parent process
LONG pcPriClassBase; // Base priority of process's threads
DWORD dwFlags;
WCHAR szExeFile[MAX_PATH]; // Path
} PROCESSENTRY32W;
MAX_PATH should be 260. My guess is that you have redefined MAX_PATH or you have put the wrong #pragma statement somewhere. Or there is something weird happening. Try restarting Windows (use Restart instead of shutdown/start)
Also, zero the memory with PROCESSENTRY32 pt = {0}
PROCESSENTRY32 pt = { 0 };
pt.dwSize = sizeof(PROCESSENTRY32);
if (!Process32First(hsnap, &pt))
{
DWORD err = GetLastError();
std::cout << "Process32First failed\n";
std::cout << pt.dwSize << " GetLastError : " << err << "\n";
CloseHandle(hsnap);
return DWORD(-1);
}
The only expected GetLastError is ERROR_NO_MORE_FILES as shown in Windows documentation. If the error is something else, it means the function has totally failed.
If your project is Unicode, as it should be, consider avoiding those T macros. Just use GetProcessId(L"notepad.exe"); and LPCWSTR etc.
Ps, I ran your code and it was fine in my computer. The only difference was sizeof(PROCESSENTRY32)