Thread: how to write a null character to a file

You try the following code

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 50

int main()
{
  FILE *pFile = NULL;
  char *filename = "test_write.txt";
  char buffer[80] = "this is for testing ";//this is the data i am going to write into the file
  int buffer_size = BUFFER_SIZE;

  size_t str_length = 0;

  pFile = fopen(filename, "w"); //opening the file for writing
  if(pFile == NULL)//checking the error in open
  {
    printf("Error opening %s for writing. Program terminated.", filename);
    abort();
  }

  str_length = strlen(buffer);
  fwrite(buffer, str_length, 1, pFile); //writing the string to the file

  fclose(pFile);
  printf("\nFile write complete\n");

  //reading that data from file
  pFile = fopen("test_write.txt","r"); //opening the file for reading
  if(pFile == NULL)
  {
    printf("Error opening %s for writing. Program terminated.", filename);
    abort();
  }
  char data[1024];
  memset(data,'\0',sizeof(data));//initializing with nulls o avoid buffer problems
  fread(data,sizeof(char),34,pFile);//reading the data what i have written to file
  fclose(pFile);
  printf("%s\n",data);//this prints this is for testing


  pFile = fopen(filename, "w"); //again opening for writing
  if(pFile == NULL)
  {
    printf("Error opening %s for writing. Program terminated.", filename);
    abort();
  }
  memset(data,'\0',sizeof(data)); //array is initialized with null

  str_length = strlen(buffer);
  fwrite(data, str_length, 1, pFile); //writing that null data
  fclose(pFile);
  printf("\nNull File write complete\n");

  //reading that data from file
  pFile = fopen("test_write.txt","r"); //now opening for reading the null data
  if(pFile == NULL)
  {
    printf("Error opening %s for writing. Program terminated.", filename);
    abort();
  }
  memset(data,'\0',sizeof(data));
  fread(data,sizeof(char),34,pFile); //reading the data to the "data" buffer. Now it contains the null what we have written
  fclose(pFile);
  printf("%s\n",data); //this will print nothing because that is null



}

Actually the second argument of write should be a string .But you tried to write a character.Because of that only you can not write the '\0'.You need to give that null as a string.

Code:

     write(fd, "\0",1);

Now you open the file in vim editor you will see a character like ^@