fork() and execve()

Alf829 · 08-01-2003, 11:55 AM

Hi all,

In C, if I fork() a process, how could I get execve() to execute the program I specify on the new child process rather than the parent process?

Does it have something to do with the return values?

Thanks in advance for any help.

Cheers,
alf829

shishir · 08-01-2003, 12:38 PM

hi,
first a small piece of CODE
{
pid_t pid;

if ( (pid = fork()) == 0)
{
//in the child process
execve(desired proggy.....);//run the desired program in
//childs addresss space

}

now the explanation: fork returns twice , once in child (with value
'0') and once in the parent (with the pid of child process)..
when you are inide the child process, you can do an exec and run the desired program in the child process....

simple...
now...well..sort o yes, it has to do somethin with the return valuse...but those of fork,,bcoz, if fork returns '0' it means child is ready to run , otherwise the parent continues on its path....
}

kev82 · 08-01-2003, 12:38 PM

yes it is related to the return values. a simple check of the man page says that fork returns -1 on error, 0 to the child, and the pid of the child to the parent so something like the following:

Code:

pid_t child;

if((child = fork()) == -1) {
    //error occured
}

if(child == 0) {
    //we're inside the child so exec here
} else {
    //we're in the parent so continue with parent stuff
}

Alf829 · 08-02-2003, 10:18 AM

Thank you both for your help

The thing I wasn't getting was how to reference to the child rather than the parent and you've provided the perfect answers

Cheers,
alf829