getline check if line is whitespace

Question

Is there an easy way to check if a line is empty. So i want to check if it contains any white space such as \r\n\t and spaces.

Thanks

Answer 1

Given a char *x=" "; here is what I can suggest:

bool onlyspaces = true;
for(char *y = x; *y != '\0'; ++y)
{
    if(*y != '\n') if(*y != '\t') if(*y != '\r') if(*y != ' ') { onlyspaces = false; break; }
}

Answer 2

You can use the isspace function in a loop to check if all characters are whitespace:

int is_empty(const char *s) {
  while (*s != '\0') {
    if (!isspace(*s))
      return 0;
    s++;
  }
  return 1;
}

This function will return 0 if any character is not whitespace (i.e. line is not empty), or 1 otherwise.

Answer 3

If a string s consists only of white space characters then strspn(s, " \r\n\t") will return the length of the string. Therefore a simple way to check is strspn(s, " \r\n\t") == strlen(s) but it will traverse the string twice. You can also write a simple function that would look at the string only once:

bool isempty(const char *s)
{
  while (*s) {
    if (!isspace(s)) return false;
    s++;
  }
  return true;
}

Answer 4

Consider the following example:

#include <iostream>
#include <ctype.h>

bool is_blank(const char* c)
{
    while (*c)
    {
       if (!isspace(*c))
           return false;
       c++;
    }
    return false;
}

int main ()
{
  char name[256];

  std::cout << "Enter your name: ";
  std::cin.getline (name,256);
  if (is_blank(name))
       std::cout << "No name was given." << std:.endl;


  return 0;
}

Answer 5

I won't check for '\0' since '\0' is not space and the loop will end there.

int is_empty(const char *s) {
  while ( isspace( (unsigned char)*s) )
          s++;
  return *s == '\0' ? 1 : 0;
}