In "Why? Motivating The API", some problems

[eric49861]

When I write code in "p4.c" like:

close(STDOUT_FILENO);
open("./info.output", O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);

I can't get the output of another programme which i want to execute in the subprocess with system call "execvp" from "info.output", but when i write the above code in another file (like "wc.c"), it recovers normal. So, i want to know whether i write wrong code or the book with something wrong.

all code i write: p2.c

#include "stdio.h"
#include "stdlib.h"
#include "unistd.h"
#include "string.h"
#include "sys/wait.h"
#include "fcntl.h"

int main(int argc, char **argv){
    printf("hello world (pid:%d)\n", (int)getpid());
    int rc = fork();
    if(rc < 0){
        fprintf(stderr, "fork failed\n");
        exit(1);
    }else if(rc == 0){
        printf("hello, I am child (pid:%d)\n", (int)getpid());
        //if i write them here, i can't get output from info.output
        //close(STDOUT_FILENO);
        //open("./info.output", O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);
        char *myargs[3];
        myargs[0] = strdup("./test");

        if(myargs[0] == NULL){
            fprintf(stderr, "malloc failed");
        }

        myargs[1] = strdup("--parameter");
        if(myargs[1] == NULL){
            fprintf(stderr, "malloc failed");
        }

        myargs[2] = NULL;
        execvp(myargs[0], myargs);
        printf("this statement shouldn't be executed");
    }else{
        //wait subprocess to finish, return pid of subprocess
        int wc = wait(NULL);
        printf("%d\n", wc);
        printf("hello, I am parent of %d (pid:%d)\n", rc, (int)getpid());
    }
    return 0;
}

test.c

#include "stdio.h"
#include "stdlib.h"
#include "unistd.h"
#include "string.h"
#include "sys/wait.h"
#include "fcntl.h"

int main(int argc, char **argv){
    if(argc == 1){
        fprintf(stderr, "need a argument but no parameter");
        exit(1);
    }
//when i write them here, it's normal
    close(STDOUT_FILENO);
    open("./info.output", O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);
    for(int i = 1; i < argc; i++){
        printf("%s\n", argv[i]);
    }
    return 0;
}