Taking a snapshot, viewing processes
This code example retrieves a list of running processes. First, the GetProcessList function takes a snapshot of currently executing processes in the system. To do that, it uses the CreateToolhelp32Snapshot function, and then it walks through the list recorded in the snapshot by using Process32First and Process32Next. For each process in turn, GetProcessList calls the ListProcessModules function, which is described in Traversing the module list, and the ListProcessThreads function, which is described in Traversing the thread list.
A simple error-reporting function, printError, displays the reason for any failures (which typically result from security restrictions). For example, OpenProcess fails for the Idle and CSRSS processes because their access restrictions prevent user-level code from opening them.
To follow along with the code example, use Visual Studio to create a new project from the C++ Console App project template, and add the code below to it.
#include <windows.h>
#include <tlhelp32.h>
#include <tchar.h>
#include <stdio.h>
// Forward declarations:
BOOL GetProcessList( );
BOOL ListProcessModules( DWORD dwPID );
BOOL ListProcessThreads( DWORD dwOwnerPID );
void printError( TCHAR const* msg );
int main( void )
{
GetProcessList( );
return 0;
}
BOOL GetProcessList( )
{
HANDLE hProcessSnap;
HANDLE hProcess;
PROCESSENTRY32 pe32;
DWORD dwPriorityClass;
// Take a snapshot of all processes in the system.
hProcessSnap = CreateToolhelp32Snapshot( TH32CS_SNAPPROCESS, 0 );
if( hProcessSnap == INVALID_HANDLE_VALUE )
{
printError( TEXT("CreateToolhelp32Snapshot (of processes)") );
return( FALSE );
}
// Set the size of the structure before using it.
pe32.dwSize = sizeof( PROCESSENTRY32 );
// Retrieve information about the first process,
// and exit if unsuccessful
if( !Process32First( hProcessSnap, &pe32 ) )
{
printError( TEXT("Process32First") ); // show cause of failure
CloseHandle( hProcessSnap ); // clean the snapshot object
return( FALSE );
}
// Now walk the snapshot of processes, and
// display information about each process in turn
do
{
_tprintf( TEXT("\n\n=====================================================" ));
_tprintf( TEXT("\nPROCESS NAME: %s"), pe32.szExeFile );
_tprintf( TEXT("\n-------------------------------------------------------" ));
// Retrieve the priority class.
dwPriorityClass = 0;
hProcess = OpenProcess( PROCESS_ALL_ACCESS, FALSE, pe32.th32ProcessID );
if( hProcess == NULL )
printError( TEXT("OpenProcess") );
else
{
dwPriorityClass = GetPriorityClass( hProcess );
if( !dwPriorityClass )
printError( TEXT("GetPriorityClass") );
CloseHandle( hProcess );
}
_tprintf( TEXT("\n Process ID = 0x%08X"), pe32.th32ProcessID );
_tprintf( TEXT("\n Thread count = %d"), pe32.cntThreads );
_tprintf( TEXT("\n Parent process ID = 0x%08X"), pe32.th32ParentProcessID );
_tprintf( TEXT("\n Priority base = %d"), pe32.pcPriClassBase );
if( dwPriorityClass )
_tprintf( TEXT("\n Priority class = %d"), dwPriorityClass );
// List the modules and threads associated with this process
ListProcessModules( pe32.th32ProcessID );
ListProcessThreads( pe32.th32ProcessID );
} while( Process32Next( hProcessSnap, &pe32 ) );
CloseHandle( hProcessSnap );
return( TRUE );
}
BOOL ListProcessModules( DWORD dwPID )
{
HANDLE hModuleSnap = INVALID_HANDLE_VALUE;
MODULEENTRY32 me32;
// Take a snapshot of all modules in the specified process.
hModuleSnap = CreateToolhelp32Snapshot( TH32CS_SNAPMODULE, dwPID );
if( hModuleSnap == INVALID_HANDLE_VALUE )
{
printError( TEXT("CreateToolhelp32Snapshot (of modules)") );
return( FALSE );
}
// Set the size of the structure before using it.
me32.dwSize = sizeof( MODULEENTRY32 );
// Retrieve information about the first module,
// and exit if unsuccessful
if( !Module32First( hModuleSnap, &me32 ) )
{
printError( TEXT("Module32First") ); // show cause of failure
CloseHandle( hModuleSnap ); // clean the snapshot object
return( FALSE );
}
// Now walk the module list of the process,
// and display information about each module
do
{
_tprintf( TEXT("\n\n MODULE NAME: %s"), me32.szModule );
_tprintf( TEXT("\n Executable = %s"), me32.szExePath );
_tprintf( TEXT("\n Process ID = 0x%08X"), me32.th32ProcessID );
_tprintf( TEXT("\n Ref count (g) = 0x%04X"), me32.GlblcntUsage );
_tprintf( TEXT("\n Ref count (p) = 0x%04X"), me32.ProccntUsage );
_tprintf( TEXT("\n Base address = 0x%08X"), (DWORD) me32.modBaseAddr );
_tprintf( TEXT("\n Base size = %d"), me32.modBaseSize );
} while( Module32Next( hModuleSnap, &me32 ) );
CloseHandle( hModuleSnap );
return( TRUE );
}
BOOL ListProcessThreads( DWORD dwOwnerPID )
{
HANDLE hThreadSnap = INVALID_HANDLE_VALUE;
THREADENTRY32 te32;
// Take a snapshot of all running threads
hThreadSnap = CreateToolhelp32Snapshot( TH32CS_SNAPTHREAD, 0 );
if( hThreadSnap == INVALID_HANDLE_VALUE )
return( FALSE );
// Fill in the size of the structure before using it.
te32.dwSize = sizeof(THREADENTRY32);
// Retrieve information about the first thread,
// and exit if unsuccessful
if( !Thread32First( hThreadSnap, &te32 ) )
{
printError( TEXT("Thread32First") ); // show cause of failure
CloseHandle( hThreadSnap ); // clean the snapshot object
return( FALSE );
}
// Now walk the thread list of the system,
// and display information about each thread
// associated with the specified process
do
{
if( te32.th32OwnerProcessID == dwOwnerPID )
{
_tprintf( TEXT("\n\n THREAD ID = 0x%08X"), te32.th32ThreadID );
_tprintf( TEXT("\n Base priority = %d"), te32.tpBasePri );
_tprintf( TEXT("\n Delta priority = %d"), te32.tpDeltaPri );
_tprintf( TEXT("\n"));
}
} while( Thread32Next(hThreadSnap, &te32 ) );
CloseHandle( hThreadSnap );
return( TRUE );
}
void printError( TCHAR const* msg )
{
DWORD eNum;
TCHAR sysMsg[256];
TCHAR* p;
eNum = GetLastError( );
FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
NULL, eNum,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
sysMsg, 256, NULL );
// Trim the end of the line and terminate it with a null
p = sysMsg;
while( ( *p > 31 ) || ( *p == 9 ) )
++p;
do { *p-- = 0; } while( ( p >= sysMsg ) &&
( ( *p == '.' ) || ( *p < 33 ) ) );
// Display the message
_tprintf( TEXT("\n WARNING: %s failed with error %d (%s)"), msg, eNum, sysMsg );
}