getline check if line is whitespace

问题

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

回答1:

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((unsigned char)*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.

回答2:

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 this will traverse the string twice. You can also write a simple function that would traverse at the string only once:

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

回答3:

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;
}

回答4:

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; }
}

回答5:

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;
}

回答6:

My suggestion would be:

int is_empty(const char *s)
{
    while ( isspace(*s) && s++ );
    return !*s;
}

with a working example.

Loops over the characters of the string and stops when
- either a non-space character was found,
- or nul character was visited.
Where the string pointer has stopped, check if the contains of the string is the nul character.

In matter of complexity, it's linear with O(n), where n the size of the input string.

回答7:

For C++11 you can check is a string is whitespace using std::all_of and isspace (isspace checks for spaces, tabs, newline, vertical tab, feed and carriage return:

std::string str = "     ";
std::all_of(str.begin(), str.end(), isspace); //this returns true in this case

if you really only want to check for the character space then:

std::all_of(str.begin(), str.end(), [](const char& c) { return c == ' '; });

来源：https://stackoverflow.com/questions/3981510/getline-check-if-line-is-whitespace

标签

whitespace

getline