android seems not support syscall,open()

Question

android is a kind of linux,and it must support the posix.But,when it seems not support the syscall,open(). Here is the code for testing,and i compile it via NDK:

#include <unistd.h>
#include <stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>

void main(){
    int fd;
    char pathname[128] = "/data/pwrite.txt";
    fd = open(pathname, O_WRONLY);
    if(fd==-1){
        printf("open fail.\n");

    }
    perror("/data/pwrite.txt");
}

and the following is the prompt that comes from android:

kaiwii@ubuntu:~$ adb shell /data/pwrite/test1
open fail.
/data/pwrite.txt: No such file or directory

Instead of just printing `"open fail"`, print the actual error instead. You can do that either by printing out `errno` or the string returned by `strerror`, or using the `perror` function. — Some programmer dude, May 28 '12 at 08:04
kaiwii@ubuntu:~$ adb shell /data/pwrite/test1 open fail. /data/pwrite.txt: No such file or directory — kaiwii ho, May 28 '12 at 08:09
@Joachim Pileborg i use the perror to print the error,and the above is what it prompt.But,i feel confused that why not the open() create the file yet.thx — kaiwii ho, May 28 '12 at 08:10
have you visited [this](http://stackoverflow.com/q/1992953/996493) ? @kaiwiiho — Lucifer, May 28 '12 at 08:22

score 1 · Answer 1 · answered May 28 '12 at 08:01

1

I think the problem is not the syscall open() but the fact that your are trying to access /data. This folder is accessible only for rooted mobiles or in the emulator. Have you tried to put the file into the /sdcard folder?

answered May 28 '12 at 08:01

Blackbelt

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score 1 · Accepted Answer · answered May 28 '12 at 08:21

1

I think that the problem is in the flags - you only use O_WRONLY. But if a file does not exist you should also create it using O_CREAT flag. So if a file does not exist you should call:

fd = open(pathname, O_WRONLY | O_CREAT);

answered May 28 '12 at 08:21

Yury

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android seems not support syscall,open()

2 Answers2