Using execvp with Input,Output and redirection

Question

In a C program, let's say i wann use Exec functions for executing a given program, for example if i wanna just try ls -l i'll do something like

args[0]="ls";
args[1]="-l";
args[2]=NULL;

...
execvp("ls", args); 

and it's all fine. Now what if i wanna also add the redirection to a file (or to stderr)? I'm stuck, it's obvious that adding >log.txt as a 3rd entry in the array won't work, but I don't know how to proceed.

And also, what if I wanna pass some Input parameters? What if i wanna execute a GCC command like "gcc -o out in redirection>log.txt" ?

[update from comment:]

It's a C program that simulate a shell which can "run strings", string that contains a command, a list o parameters, input and a redirection.

Answer 1

Just set up your file descriptors as the exec-d process shall find them and then do the exec.
For that you need open, dup2 and close.

All functions in the exec-family just replace the current process with whatever one you say.

Answer 2

Run the command in a shell:

char * args[] = {
  "sh",
  "-c",
  "ls -l >out.ls 2>err.ls <in.ls",
  NULL
};

...

execvp(args[0], args); 
perror("execvp() failed");