Help with understanding C code in my text
I am reading a book on operating systems before I go on to try and learn C. The book often lists code to illustrate points, and while it is not mandatory I understand it, I would like to so I can better learn from it. Both of the following codes were presented:
Code:
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
pid-t pid;
/* fork a child process */
pid = fork();
if (pid < 0) {/* error occurred */
fprintf(stderr, "Fork Failed");
exit (-1) ;
}
else if (pid == 0} {/* child process */
execlpf"/bin/Is","Is",NULL);
}
else {/* parent process */
/* parent will wait for the child to complete */
wait(NULL);
printf("Child Complete");
exit (0) ;
This is supposed to represent how a child process that is running a copy of a program from the parent process looks in C coding for unix. I understand some things, like the idea of a fork statement, and the text tells me what the equation tries to accomplish. More direct and specific insight would be great though.
The second equation below is supposed to represent how to create a child process function. How though is yet unclear to me. I have been told that it has something to do with microsoft paint as a shared resource, but they were very vague:
Code:
#include <stdio.h> i
#include <windows.h>
int main(VOID)
{
STARTUPINFO si;
PROCESS_INFORMATION pi;
// allocate memory
ZeroMemory(&si, sizeof (si)) ;
si.cb = sizeof (si) ;
ZeroMemory(&pi, sizeof(pi));
// create child process
if (!CreateProcess(NULL, // use command line
"C:\\WINDOWS\\system32\\mspaint.exe", // command line
NULL, // don't inherit process handle
NULL, // don't inherit thread handle
FALSE, // disable handle inheritance
0, //no creation flags
NULL, // use parent's environment block
NULL, // use parent's existing directory
&si,
&pi})
{
fprintf(stderr, "Create Process Failed");
return -1;
}
// parent will wait for the child to complete
WaitForSingleObject(pi.hProcess, INFINITE);
printf("Child Complete");
// close handles
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
}
Thanks a lot in advanced
