You need:
#include <ctype.h>
Linux Man Pages
man7.org › linux › man-pages › man3 › isspace.3p.html
isspace(3p) - Linux manual page
The isspace() and isspace_l() functions shall test whether c is a character of class space in the current locale, or in the locale represented by locale, respectively; see the Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale. The c argument is an int, the value of which the application ...
Programiz
programiz.com › c-programming › library-function › ctype.h › isspace
C isspace() - C Standard Library
#include <stdio.h> #include <ctype.h> int main() { char c; int result; printf("Enter a character: "); scanf("%c", &c); result = isspace(c); if (result == 0) { printf("Not a white-space character."); } else { printf("White-space character."); } return 0; }
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Linux Man Pages
linux.die.net › man › 3 › isspace
isspace(3): char classification routines - Linux man page
These functions check whether c, which must have the value of an unsigned char or EOF, falls into a certain character class according to the current locale.
W3Schools
w3schools.com › c › ref_ctype_isspace.php
C ctype isspace() Function
char c = ' '; if (isspace(c)) { printf("%c is whitespace", c); } else { printf("%c is not whitespace", c); } Try it Yourself »
GeeksforGeeks
geeksforgeeks.org › c language › isspace-in-c
isspace() in C - GeeksforGeeks
September 13, 2024 - It is the character to be tested. The isspace() function returns an integer value that tells whether the passed parameter is a whitespace character or not.
TutorialsPoint
tutorialspoint.com › c_standard_library › c_function_isspace.htm
C Library - isspace() function
#include <stdio.h> #include <ctype.h> int main () { int var1 = 't'; int var2 = '1'; int var3 = ' '; if( isspace(var1) ) { printf("var1 = |%c| is a white-space character\n", var1 ); } else { printf("var1 = |%c| is not a white-space character\n", var1 ); } if( isspace(var2) ) { printf("var2 = |%c| is a white-space character\n", var2 ); } else { printf("var2 = |%c| is not a white-space character\n", var2 ); } if( isspace(var3) ) { printf("var3 = |%c| is a white-space character\n", var3 ); } else { printf("var3 = |%c| is not a white-space character\n", var3 ); } return(0); }
Top answer 1 of 2
10
You need:
#include <ctype.h>
2 of 2
9
You need #include <ctype.h>.
However make sure you read the documentation carefully. Its interface is unintuitive, for historical reasons.
It's designed to work only on a value from 0 to UCHAR_MAX (usually 255) -- the same sort of value that is returned by the getchar() function. For example:
int ch = getchar();
if ( isspace(ch) )
Do not use it with a char. If you have a char that you want to check for whitespace, it must be converted to be in the expected range; e.g. by a cast to (unsigned char):
char ch = 't';
if ( isspace( (unsigned char)ch ) )
The same goes for all of the other is* functions in ctype.h
The Open Group
pubs.opengroup.org › onlinepubs › 009696599 › functions › isspace.html
isspace
The c argument is an int, the value ... If the argument has any other value, the behavior is undefined. The isspace() function shall return non-zero if c is a white-space character; otherwise, it shall return 0....
NetBSD
man.netbsd.org › isspace.3
isspace(3) - NetBSD Manual Pages
ISSPACE(3) NetBSD Library Functions Manual ISSPACE(3) NAME isspace -- white-space character test LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <ctype.h> int isspace(int c); DESCRIPTION The isspace() function tests for the standard white-space characters for which isalnum(3) is false.
Man Pages
manpages.org › isspace
man isspace (1): test for a white-space character
man isspace (1): The isspace() function shall test whether c is a character of class space in the program's current locale; see the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 7, Locale. The c argument is an int, the value of which the application shall ensur
MKSSoftware
mkssoftware.com › docs › man3 › isspace.3.asp
isspace(), isspace_l() -- tests if character is a white-space character
isgraph() is true. The standard white-space characters are the following: space, tab, carriage-return, newline, vertical tab, and form-feed. In the C locale, isspace() returns true only for the standard white-space characters.
Linux Man Pages
man7.org › linux › man-pages › man3 › isspace.3.html
isalpha(3) - Linux manual page
The list below explains the operation of the functions without the "_l" suffix; the functions with the "_l" suffix differ only in using the locale object locale instead of the current locale. isalnum() checks for an alphanumeric character; it is equivalent to (isalpha(c) || isdigit(c)). isalpha() checks for an alphabetic character; in the standard "C" locale, it is equivalent to (isupper(c) || islower(c)). In some locales, there may be additional characters for which isalpha() is true—letters which are neither uppercase nor lowercase. isascii() checks whether c is a 7-bit unsigned char value
Medium
medium.com › @larkm0258 › understanding-isspace-in-c-how-it-works-and-when-to-use-it-b0b51aa8851e
Understanding isspace() in C: How It Works and When to Use It | by michael lark | Medium
April 2, 2025 - What is isspace()? The isspace() function is part of the C standard library and is defined in the <ctype.h> header file. It is used to check whether a given character is a whitespace character.
cppreference.com
en.cppreference.com › c › string › byte › isspace
isspace - cppreference.com
#include <ctype.h> #include <limits.h> #include <stdio.h> int main(void) { for (int ndx = 0; ndx <= UCHAR_MAX; ++ndx) if (isspace(ndx)) printf("0xx ", ndx); } Output: 0x09 0x0a 0x0b 0x0c 0x0d 0x20 ·
W3Resource
w3resource.com › c-programming › ctype › c-isspace.php
C isspace() function
April 10, 2026 - #include <stdio.h> #include <ctype.h> int main() { char c; int result; printf("Enter a character: "); scanf("%c", &c); result = isspace(c); if (result == 0) { printf("Not a white-space character."); } else { printf("White-space character."); } return 0; }
Oracle
docs.oracle.com › cd › E86824_01 › html › E54766 › isspace-3c.html
isspace - man pages section 3: Basic Library Functions
Tests for any space, tab, carriage-return, newline, vertical-tab or form-feed (standard white-space characters) or for one of the current locale-defined set of characters for which isalnum() is false. In the “C” locale, isspace() returns true only for the standard white-space characters.
cppreference.com
en.cppreference.com › cpp › string › byte › isspace
std::isspace - cppreference.com
June 28, 2024 - #include <cctype> #include <climits> #include <iomanip> #include <iostream> int main(void) { std::cout << std::hex << std::setfill('0') << std::uppercase; for (int ch{}; ch <= UCHAR_MAX; ++ch) if (std::isspace(ch)) std::cout << std::setw(2) << ch << ' '; std::cout << '\n'; }
Ultra64
ultra64.ca › files › documentation › online-manuals › man-v5-1 › nusystem › function › isspace.htm
isspace - Macro
#include <ctype.h> int isspace(int c); Arguments · c character code · Return Value · An int value that is either a value other than zero (true) or zero (false) Description ·
O'Reilly
oreilly.com › library › view › c-in-a › 0596006977 › re129.html
isspace - C in a Nutshell [Book]
December 16, 2005 - NameisspaceSynopsisAscertains whether a given character produces space#include <ctype.h> intisspace( int c );The function isspace() tests whether its character argument... - Selection from C in a Nutshell [Book]
Authors Peter PrinzTony Crawford
Published 2005
Pages 618
CS50
manual.cs50.io › 3 › isspace
isspace - CS50 Manual Pages
#include <cs50.h> #include <ctype.h> #include <stdio.h> int main(void) { char c = get_char("Input: "); if (isspace(c)) { printf("Your input is whitespace.\n"); } else { printf("Your input is not whitespace.\n"); } }