in gcc how to read the presence of a blank line

[ishandutta2007]

in gcc how to read a blank line ie a string of length 0.

my code:

#include<stdio.h>
#include<string.h>
#include<string>
using namespace std;

int main()
{ int n;
  char a[151];    
  scanf("%d",&n);
  while(n--)
	{	
		gets(a);
		if(strlen(a)==0)printf("null string\n");
	}
  return 0;
}

but its reding string a as null string at time i read n and hit a enter.

[coopstah13]

you are writing c++ code based on your use of namespaces no?

why do you include string 2 times, only include it once, you don't need .h since you are using namespace std

you should use cin and getline in c++ imo

[Cabhan]

If you're using C++, as coopstah says, you should use cin instead of gets(). Even if you're using C, gets() is a very dangerous function: you should use fgets() instead (it allows you to give a string length, which avoids buffer overflow attacks).

Anyway, I think that your problem is related to scanf(). If your input to the first prompt (for n) is "4\n" (that is, "4" followed by enter), the 4 gets put into n, but the newline is left in the stream. Therefore, gets() sets a to a blank string, because the next character is a newline.

You need to change your scanf() to:

scanf("%d\n", &n);

As a side note, a more efficient way to check for an empty string is:

if(*a == '\0')
    printf("null string\n");

This is because if a is not an empty string, this doesn't require traversing it to find out its length.

[ultimatelinux]

equivalent of a white space is '\0'
a new line '\n'
a tab '\t'

[Cabhan]

That is not quite correct. \0 indicates the end of a string: it is a null byte. Whitespace is indicated by the equivalent character: ' ' for a space, \n for a newline, or \t for a tab.