Question

Following program:

#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>

int main() {
  fclose( stderr );
  printf( "%d\n", fileno( stderr ) );
  return 0;
}

shows -1 on ubuntu 11.04 and 2 on ICS 4.0.3 emulator. Can’t find any info about this issue – can i make this code work similar on both platforms? freopen on stderr has same problem.

Update:

Previous small program demonstrates the cause of actual problem i faced with: if i try to freopen stderr to file in inexistent directory, on linux stderr is closed but on android it stays opened! And even more – if i write smth in this opened stderr file and then do fopen on some other file, text i printed to stderr is written to this opened file.

So, this program:

#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>

# define LOGD( ... ) printf( __VA_ARGS__ ); printf( "\n" )

# ifdef ANDROID
#   define HOMEDIR "/data/data/com.myapp/" // for android
# else
#   define HOMEDIR "/home/darkmist/" // for linux
# endif

# define _T( x ) x

void TestFreopen_mkdir() {
  int mkdirres = mkdir( HOMEDIR "1.d", 0777 );
  LOGD(_T("TestFreopen mkdirres=0x%08x"),mkdirres);
}

void TestFreopen() {
  LOGD(_T("TestFreopen begin"));

  LOGD(_T("TestFreopen stderr=0x%08x"),fileno(stderr));
  fprintf(stderr,"fprintf_1 to stderr\n");

  // TestFreopen_mkdir(); // case 1

  if ( NULL == freopen( HOMEDIR "1.d/1", "w", stderr ) ) {
    LOGD( "freopen failed" );
    if ( -1 != fileno( stderr ) ) {
      fclose( stderr );
      LOGD( "freopen closed" );
    }
  }

  LOGD(_T("TestFreopen stderr=0x%08x"),fileno(stderr));
  fprintf(stderr,"fprintf_2 to stderr\n");

  TestFreopen_mkdir(); // case 2

  FILE* fopen_file = fopen( HOMEDIR "1.d/2", _T( "wb" ) );

  LOGD(_T("TestFreopen fopen_file=0x%08x"),fileno(fopen_file)); // same as for reopened stderr!!

  fprintf(stderr,"fprintf_3 to stderr\n");
  fprintf(fopen_file,"fprintf_1 to fopen_file\n");
  fflush(fopen_file);

  LOGD(_T("TestFreopen end"));
}

int main() {
  TestFreopen();
  return 0;
}

shows this on linux:

$ ./a.out
TestFreopen begin
TestFreopen stderr=0x00000002
fprintf_1 to stderr
freopen failed
TestFreopen stderr=0xffffffff
TestFreopen mkdirres=0x00000000
TestFreopen fopen_file=0x00000002
TestFreopen end

$ cat ~/1.d/2 
fprintf_1 to fopen_file

and this on android:

$ adb push ./a.out /data/data/com.myapp
573 KB/s (34635 bytes in 0.058s)

$ adb shell run-as com.myapp /data/data/com.myapp/a.out
TestFreopen begin
TestFreopen stderr=0x00000002
fprintf_1 to stderr
freopen failed
freopen closed
TestFreopen stderr=0x00000002
TestFreopen mkdirres=0x00000000
TestFreopen fopen_file=0x00000002
TestFreopen end

$ adb shell run-as com.myapp cat /data/data/com.myapp/1.d/2
fprintf_3 to stderr
fprintf_1 to fopen_file

Answer 1

It doesn’t make any sense to try to use stderr after closing it, on any platform.