Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 243
  • Last Modified:

Null on non-zero entry but not null on zero entry in binary file

myFile.txt is a binary file:

Followed is the result of od -Ax -tx1 myFile.txt:
000000 68 01 00 00 a0 05 00 00 48 00 00 00 38 05 00 00

Followed is the complete code

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>//O_RDONLY


int main(int argc, char *argv[])
{
      if (argc!=3){
            printf("Please enter exactly three arguments.\n");
      }else{
                 //myFile.txt is being memory map
            int f=open(myFile.txt,O_RDONLY);
            int n=lseek(f,0,SEEK_END);
            char * mf=mmap(0,n,PROT_READ,MAP_PRIVATE,f,0);
            int i;
            for (i=0;i<16;i++){
                  if (mf[i]=='\0'){
                      printf("File content= %p\n",mf[i]);
                  }else{
                        printf("Nothing\n");
                  }
            }
            
      }

   return 0;
}
Result of execution
===============
999
999
File content= (nil)
File content= (nil)
999
999
File content= (nil)
File content= (nil)
999
File content= (nil)
File content= (nil)
File content= (nil)
999
999
File content= (nil)
File content= (nil)

My Question is
I suppose it is mf[i]!='\0' on non-zero entry, and mf[i]=='\0' on zero entry, but the result is
mf[i]=='\0' on non-zero entry, and mf[i]!='\0' on zero entry, what is the reason?

0
william007
Asked:
william007
  • 3
  • 2
1 Solution
 
0xC0DEB07Commented:
There is difference between '\0' and '0' ;)
0
 
william007Author Commented:
Can you explain what happening on for getting that result?
0
 
sunnycoderCommented:
I dont see a single print of "nothing" in the output!!
Also the code would not compile since filename is not in quotes ... Is this really the exact code and output?
0
Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

 
william007Author Commented:
Sorry, correction as followed
1. Put the filename in the quote

2. Result
=====
Nothing
Nothing
File content= (nil)
File content= (nil)
Nothing
Nothing
File content= (nil)
File content= (nil)
Nothing
File content= (nil)
File content= (nil)
File content= (nil)
Nothing
Nothing
File content= (nil)
File content= (nil)
0
 
sunnycoderCommented:
This output is consistent with the code

               if (mf[i]=='\0'){
                   printf("File content= %p\n",mf[i]);
               }else{
                    printf("Nothing\n");
               }

you print value only if == '\0' ... '\0' is same as 0
0
 
william007Author Commented:
Thanks=)
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

  • 3
  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now