Rewrite C Function: isspace

Last Updated : 10 July, 2022 · 2 min read

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Today we are going to overview isspace function and its workings in C programming language. This tutorial is split up into three following parts:

Structure of isspace:

Declaration: int isspace(int c);

Return: non-zero value if int c is a whitespace value. Otherwise, 0.

Parameter list:
(int c) - the character that is checked to determine the return value.

Header file: <ctype.h>.

1. So, what is the isspace function in C?

This function in C language checks if the passed char value is a white-space character. The return value of isspace is an int.

If the argument is a white-space value, function isspace returns non-zero value.

If the argument is not a white-space value, the isspace function returns 0.

The isspace function is defined in the <ctype.h> library. To use this function, we have to include this header file into the C program (e.g. #include <ctype.h> ).

Example 1: Usage of the isspace function in C.

# include <ctype.h>
# include <stdio.h>

int main( void )
printf ( "%d", isspace ( '\n' ));
printf ( "%d", isspace ( '1' ));
return ( 0 );

Possible output:


2. And how to rewrite the isspace function in C?

Consider the code snippet below for a second:

Example 2: Rewritten isspace function in C

int our_isspace ( int c )
if ( ( c >= 9 && c <= 13 ) || ( c == 32 ) )
return ( 1 );
return ( 0 );

The our_isspace function above takes one parameter. Since this parameter c is of int type, arguments of char type (when sent as arguments to this function) get implicitly typecasted to an according numerical value.

On the line 3 we are checking if the received value of c is in the range of [9,13] or 32. If this conditional statement returns true, it means that the value is a white-space character (' ', '\n', '\r', '\t', '\v', 'f') and 1 is returned. Otherwise 0 is returned, indicating that the value of c is not a white-space character.

3. Quiz of the reader's knowledge

Quiz : Rewrite C Function

1What is the return value of isspace(13)?

2What is the return value of isspace('\n')?

3In which library is isspace defined?

quiz completed!


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