Run several copies of some program from c++ program - c++

Question

What I need to do is to run (for example) 6 copies (independent processes) of example.exe (what is also my program) with different command line arguments from my Main program. This copies should work at the same time. I'm using code like this:
const int NumberOfProcesses= 6;
STARTUPINFO si[NumberOfProcesses];
PROCESS_INFORMATION pi[NumberOfProcesses];
srand((unsigned)time(NULL));
for(int i=0;i<NumberOfProcesses;i++)
{
char fname[MAX_PATH];
strncpy(fname,"\"",1);
fname[1] = '\0';
strcat(fname,"d:\\test\\example.exe");
strcat(fname,"\"");
int id = i;
strcat(fname," ");
strcat(fname,(std::to_string(id)).c_str());
int count = (rand()%1000) + 1;
strcat(fname," ");
strcat(fname,(std::to_string(count)).c_str());
int lb = 13;
strcat(fname," ");
strcat(fname,(std::to_string(lb)).c_str());
int ub = 666;
strcat(fname," ");
strcat(fname,(std::to_string(ub)).c_str());
printf(fname);
cout<<"\n";
//Here in fname I have correct command, that runs properly
bool t = false;
t=CreateProcess( NULL, // No module name (use command line)
(LPSTR)fname, // Command line CharToLPWSTR(fname2)
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si[i], // Pointer to STARTUPINFO structure
&pi[i] ); // Pointer to PROCESS_INFORMATION structure
}
So if NumberOfProcesses==0 it will run "d:\test\example.exe" 1 2 3 4 from fname. But if NumberOfProcesses==6 (or something else) zero iteration will complete properly, but others will return false. Sometimes 4th iteration runs properly.
I think this is because when zero iteration run "d:\test\example.exe" 1 2 3 4 the example.exe is busy and can not be run one more time. So I changed code to this:
bool t = false;
getchar();
for(int i=0;i<5;i++)
{
t=CreateProcess( NULL, // No module name (use command line)
(LPSTR)fname, // Command line CharToLPWSTR(fname2)
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si[i], // Pointer to STARTUPINFO structure
&pi[i] ); // Pointer to PROCESS_INFORMATION structure
if(t) break;
}
So I got some delay between starting example.exe - and it helped. All 6 copies starts and finishes, but they don't run parallel (I have output from example.exe).
But this is not the way I want my program work.
How can I avoid this problem?
Thanks.
UPD.
According to Werner Henze's answer I've just add couple of lines (to initialize STURTUPINFO) into loop
const int NumberOfProcesses= 6;
STARTUPINFO si[NumberOfProcesses];
PROCESS_INFORMATION pi[NumberOfProcesses];
for(int i=0;i<NumberOfProcesses;i++)
{
///Next two lines is important
ZeroMemory( &si[i], sizeof(si[i]) );
si[i].cb = sizeof(si);
/*Some actions*/
t=CreateProcess( NULL, // No module name (use command line)
(LPSTR)fname, // Command line CharToLPWSTR(fname2)
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si[i], // Pointer to STARTUPINFO structure
&pi[i] ); // Pointer to PROCESS_INFORMATION structure
}
And it is work fine now.
Thanks again.

Answer 1

In the cases where CreateProcess returns FALSE you should check GetLastError(). In the code that you posted you are not initializing the si array. STARUPINFO is an input paramter to CreateProcess, so you must initialize it before passing it to CreateProcess.
I guess example.exe is running so fast that they are terminated before you come to look at them. If you printf a timing value like GetTickCount() after each CreateProcess, you will see that all CreateProcess calls occur very fast.