C ctype.h isspace() Function

isspace() Function

The isspace() function in C is used to determine if a character is a white-space character. It checks if the provided character is one of the standard white-space characters defined by the locale. This function is essential in text processing where filtering or identifying space characters is required.

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Syntax of isspace()

int isspace(int c);

Parameters

Parameter	Description
c	An integer representing the character to be checked, typically cast from a char or EOF.

It is worth noting that for the default “C” locale, the white-space characters include space (' '), horizontal tab ('\t'), newline ('\n'), vertical tab ('\v'), form feed ('\f'), and carriage return ('\r'). Other locales may define additional characters as white-space, but none will classify an alphanumeric character as white-space.

Return Value

The function returns a nonzero value (true) if the character is a white-space character, and zero (false) otherwise.

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Examples for isspace()

Example 1: Checking a Single White-space Character

This example demonstrates the basic usage of isspace() by checking if a single character is a white-space.

Program

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

int main() {
    int ch = ' ';

    if (isspace(ch)) {
        printf("The character ' ' is a white-space character.\n");
    } else {
        printf("The character ' ' is not a white-space character.\n");
    }

    return 0;
}

Explanation:

1. A character variable is assigned the space character (' ').
2. The isspace() function checks if this character is a white-space.
3. Since a space is a white-space, the program prints that it is a white-space character.

Program Output:

The character ' ' is a white-space character.

Example 2: Differentiating White-space from Non White-space Characters

This example checks multiple characters to identify which ones are white-space characters and which ones are not.

Program

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

int main() {
    char testChars[] = " \tA\nB";
    int i = 0;

    while (testChars[i] != '\0') {
        if (isspace(testChars[i])) {
            printf("'%c' is a white-space character.\n", testChars[i]);
        } else {
            printf("'%c' is not a white-space character.\n", testChars[i]);
        }
        i++;
    }

    return 0;
}

Explanation:

1. An array of characters is initialized with a space, a horizontal tab, letters, and a newline.
2. The program iterates through each character in the array.
3. For each character, isspace() is used to check if it is a white-space character.
4. The program prints the result for each character.

Program Output:

' ' is a white-space character.
'       ' is a white-space character.
'A' is not a white-space character.
'
' is a white-space character.
'B' is not a white-space character.

Example 3: Scanning a String for White-space Characters

This example demonstrates how to scan an entire string to check each character for white-space using isspace().

Program

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

int main() {
    char str[] = "Hello World!\n";
    int i = 0;

    while (str[i] != '\0') {
        if (isspace(str[i])) {
            printf("Character '%c' is a white-space character.\n", str[i]);
        } else {
            printf("Character '%c' is not a white-space character.\n", str[i]);
        }
        i++;
    }

    return 0;
}

Explanation:

1. A string containing letters, a space, and a newline is defined.
2. The program iterates through the string character by character.
3. The isspace() function checks each character to determine if it is a white-space.
4. A message is printed indicating whether each character is a white-space character or not.

Program Output:

Character 'H' is not a white-space character.
Character 'e' is not a white-space character.
Character 'l' is not a white-space character.
Character 'l' is not a white-space character.
Character 'o' is not a white-space character.
Character ' ' is a white-space character.
Character 'W' is not a white-space character.
Character 'o' is not a white-space character.
Character 'r' is not a white-space character.
Character 'l' is not a white-space character.
Character 'd' is not a white-space character.
Character '!' is not a white-space character.
Character '
' is a white-space character.