Thread: How to detect null string?

>--if a user type nothing but simply a "Enter" key then a message is shown
Since you should be using fgets for string data , simply test to see if fgets returns NULL for EOF. To check if the user simply typed return check the first character of the array for '\n', otherwise they gave you more than nothing.

Code:

#include <stdio.h>

int main ( void )
{
  char a[BUFSIZ];

  if ( fgets ( a, sizeof a, stdin ) == NULL )
    puts ( "Oops, no input read" );
  else if ( a[0] == '\n' )
    puts ( "Don't just hit enter, type something" );
  else
    printf ( "You typed \"%s\"\n", a );

  return 0;
}

-Prelude

Depends on what you mean by a NULL string:

Code:

//The pointer is NULL, no string
if(String == NULL)

Code:

//The string is empty
if(strcmp(String, "") == 0)

Code:

//If the string begins with a NULL terminator, basically the same as #2.
if(String[0] == '\0')

Code:

//If the string contains the letters NULL
if(strcmp(String, "NULL") == 0)