Read number of whitespaces for an array of characters

Question

I have to make a simple function to display the number of whitespaces in a predefined array of characters. This is my code : (please ignore the first part, only last part and whitespaces function)

#include <iostream>
#include <conio.h>
using namespace std;

int whitespaces(char[]);

void main(){
    char a[] = "Array of characters for test\n";  //Simple array of characters
    cout << "\n This is a test : " << a;
    char b[] = "\n\t Another array of character for test\n"; //Simple array with some escape sequences, \t and \n
    cout << "\n This is a test for usage of escape sequences : " << b;
    char c[] = "T E S T\n";                                   //Simple array with 8 characters and whitespaces
    cout << "\n Last test for whitespaces : "<<c;
    int ws = whitespaces(c);
    cout << "\n Number of whitespaces for the last array of characters is : "<<ws;
    _getch();
}

int whitespaces(char c[]){
    int count = 0;
    for (int n = 0; n <= sizeof(c); n++) {
        if (c[n] == ' '){
            count++;
        }
    }
        return(count);
}

Using Visual Studio express

Right now, you're only looking for a literal space character. If you want to count all white space (e.g., also tabs and new-lines) you probably want to look up `isspace`. — Jerry Coffin, Nov 09 '14 at 16:42

score 3 · Answer 1 · edited May 23 '17 at 12:20

Here's what you can use if you want all whitespace characters to be counted (not only the space character):

std::string::size_type countWs( std::string const& str )
{
    return std::count_if( std::begin(str), std::end(str),
                          [] (unsigned char c) {return std::isspace(c);} );
}

Or, alternatively,

std::size_t countWs( char const* str )
{
    std::size_t c = 0;
    while (*str)
        c += !!std::isspace((unsigned char)*str++);
    return c;
}

Demo. As to the casts to unsigned char, this question might be worth looking at.

Vlad from Moscow · Accepted Answer · 2014-11-09T16:58:18.853

1

You have to use standard C function std::strlen declared in header <cstring> instead of sizeof operator because an array passed by value to a function is implicitly converted to a pointer to its first element. Also the blank character is not the only white space character. Either you should use standard function std::isspace or std::isblank declared in header <cctype>

So the function will look like

#include <cstring>
#include <cctype>

//...

int whitespaces( const char c[] )
{
    int count = 0;
    size_t n = std::strlen( c );

    for ( size_t i = 0; i < n; i++ ) 
    {
        if ( std::isspace( c[i] ) ) ++count;
    }

    return ( count );
}

The other way is to use the characteristic of character arrays that store strings that they have the terminating zero.

In this case the function could be defined as

#include <cstring>
#include <cctype>

//...

int whitespaces( const char c[] )
{
    int count = 0;

    while ( *c )
    {
        if ( std::isspace( *c++ ) ) ++count;
    }

    return ( count );
}

Also take into account that there are standard algorithms std::count and std::count_if that can be used instead of your function.

edited Nov 09 '14 at 16:58

answered Nov 09 '14 at 16:47

Vlad from Moscow

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Your examples are both wrong. Not only because you forgot to dereference the pointer in one. – Columbo Nov 09 '14 at 16:55
@Columbo It was a typo, Thanks. And what wrong with examples? Maybe you want to say that instead of int there must be used size_t? – Vlad from Moscow Nov 09 '14 at 16:59
@VladfromMoscow No, you lack a cast to `unsigned char`. See my answer. – Columbo Nov 09 '14 at 17:00
@Columbo Why should the argument of isspace be casted to unsigned char? – Vlad from Moscow Nov 09 '14 at 17:02
@VladfromMoscow See the link in my answer. http://stackoverflow.com/questions/21805674/do-i-need-to-cast-to-unsigned-char-before-calling-toupper – Columbo Nov 09 '14 at 17:04
@VladfromMoscow No, it's not. What do you mean? Have you read the reference for `isspace`? – Columbo Nov 09 '14 at 17:08
@Columbo He uses the basic character set where all symbols are non-negative. – Vlad from Moscow Nov 09 '14 at 17:19
@VladfromMoscow ... so you wrote a general function that only works with the sample inputs provided in the question? – Columbo Nov 09 '14 at 17:21
@Columbo In fact so. But you are right in general case you need casting. Though if you use a locale then the first parameter of isspace is defined as char. – Vlad from Moscow Nov 09 '14 at 17:26

Read number of whitespaces for an array of characters

2 Answers2