Process ID of a "Stranger"

[Reiner Wilhelms]

It is rather easy to obtain the process Id of a process via the system
call getpid(), and of the parent process via getppid().
However, how can I obtain the process id of a "stranger": some other
process, running on the same machine, if I just know its name?
Of course, it is possible to call ps, and then search for the name in
its output.  I wonder if there is any system call or ugly trick which
does a simpler job, like:

{
int pid,errorcode;
 ....
errorcode =  pid_by_name("Stranger",&pid);
if (errorcode == THERE_IS_NO_ONE_WITH_THAT_NAME) 
	sprintf(stderr,"Stranger is not running\n");
 ....
}
Is there something like pid_by_name() in Unix?
Or, to put it different, what does ps do?

Thank you for any hint.

Reiner