I have a file descriptor fd, and would like to use it to write a null character \0 to the connected file. I am trying to write this using:

Code:

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

however, this doesn't seem to be writing these characters. Does anyone know how I can accomplish this? Thanks!

It is working for me.The function write returns 1 as its value which means 1 character written into the file.I tried a program.
When I opened the created file in vim editor,it showed me the character as ^@.
You execute it.

Code:

#include	<stdio.h>
#include	<stdlib.h>
#include	<fcntl.h>
#include	<sys/types.h>
#include	<sys/stat.h>
	int
main ( int argc, char *argv[] )
{
        int fd;
	if((fd=open("Temp",O_WRONLY,0777))<0)
	{
		perror("File");
		exit(1);
	}
	printf ( "No of Characters Written:%d\n", write(fd,"\0",1) );
	return 0;
}

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 ^@

That should work unless fd isn't open for writing.

Yeah,it works when fd is opened as O_WRONLY mode as well as if fd is opened for read and write mode which is O_RDWR flag in open function.

perfect. Thanks!