Check for process on multiple platforms? - c++

Question

I'm using Qt, QProcess to launch a process, but there is presently no way to use QProcess to check existing running processes.
I need a way of achieving this on multiple platforms. I have an application name that I want to look up, if its running I want to get it's PID. If it isn't running I will create an instance of it, this last bit I can do.
I'm working on a Mac and so far I've done the following:
pid_t pid = fork();
if ( pid > 0 ) {
int intStatus;
while ( (pid = waitpid(-1, &intStatus, WNOHANG)) == 0) {
system("ps -A");
qDebug() << "Still waiting!";
sleep(20);
}
qDebug() << "Exit Status %d" << WEXITSTATUS(intStatus);
}
The above executes the command and the output is dumped in the console, I need to capture this so I can process it.
Also looking for a way to achieve this on Windows platforms.

Answer 1

On Posix systems, you could capture the output of ps by using popen and then parse it. The popen part looks like this:
#include <iostream>
#include <cstdio>
int main()
{
FILE *f = popen ("ps -A", "r");
char s [1024];
while (fgets (s, sizeof (s), f))
std::cout << s;
pclose (f);
}
Live demo

Answer 2

I'm not sure how to go about this on linux or unix, but here is an example for windows.
int CheckProc(const wchar_t* procName, PROCESSENTRY32 *procEntry)
{
HANDLE hSnap;
hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
if (hSnap == INVALID_HANDLE_VALUE)
{
printf("invalid handle value %s", (char*)hSnap);
return -1;
}
procEntry->dwSize = sizeof(PROCESSENTRY32);
if (!Process32First(hSnap, procEntry))
{
printf("process32first failed");
CloseHandle(hSnap);
return -1;
}
do
{
if(wcscmp(procEntry->szExeFile, procName) == 0)
{
return 1;
}
} while (Process32Next(hSnap, procEntry));
CloseHandle(hSnap);
return 0;
}
int main()
{
PROCESSENTRY32 procEntry;
const wchar_t* procName = L"process name";
CheckProc(procName, &procEntry);
std::cout << "PID: " << procEntry.th32ProcessID;
}