尝试使用返回拒绝权限的popen函数时如何处理无效/垃圾值

Question

I'm trying to write a program that will look for files owned by user. Then print the output into a variable to manipulate it or comunicate it with some other program. The problem is when I put the directory as / , most of the early find will be permission denied. But there seems to be a NULL/garbage or something assigned to the variable even though it states that permission denied. Here are the codes:

static struct{
          char file_owned[8192][1024];
}information;

void get_file_owned(char *username)
{
  FILE *stream3;
  extern FILE *popen();
  char command[1024];
  char buff[1024];
  int i;

  sprintf(command, "find / -user %s -ls",username);
  if(!(stream3 = popen(command), "r"))){
       exit(1);
  }
  i=0;
  while(fgets(buff, sizeof(buff), stream3)!=NULL){
       sprintf(information.file_owned[i],"%s",buff); //it print something into file_owned. But I do now know what. 
       i++;
  }
  pclose(stream3);
  return;
}

int main(int argc, char **argv)
{
  static char *username;
  int i;

  username = "fikrie";
  get_file_owned(username);

  for(i=0;i<10;i++){
    printf("%s\n",information.process_owned[i]);
  }
  return 0;
 }

This is the output:

find: `/proc/1657/task/1659/ns` : Permission denied
find: `/proc/1713/task/1713/ns` : Permission denied
...
...
//There's a lot of this kind of output
...
Segmentation fault(core dumped)

I'm expecting its caused by the permission denied. Which will then just print a garbage into process_owned. How should I handle output for the permission denied? I've tried to handle a NULL inside the get_file_owned function. But it doesn't solve it.

while(fgets(buff, sizeof(buff), stream3)!=NULL){
    if(buff == NULL){
    continue;
    }
    sprintf(information.file_owned[i],"%s",buff);
    i++;
}

I've also tried to use gdb to see about the segmentation fault. This is the result:

warning: Can't read pathname for load map: Input/output error
Core was generated by `./a.out'.
Program terminated with signal 11, Segmentation fault.
#0 _IO_getline info (fp=0x9ec50b8, buf=0x2 <Address 0x2 out of bounds>, n=254, delim=10, extract_delim=1, eof=0x0) at iogetline.c:91
iogetline.c: No such file or directory.

Please take note that if I tried to run this in my home directory. /home/fikrie/Documents . There's no segmentation fault or error.

EDIT: I have also run this program as root. Change the structure way into this type:

struct{
   char file_owned[1024];
}information[1024];   //I tried changing this into 8094 also. Just in case the array for this struct is not enough. 

Answer 1

find propably returns more then 8192 lines. Therefore the while loop overflows the array file_owned .