C ctype.h isblank() Function

isblank() Function

The isblank() function in C determines if a given character is a blank character. It is primarily used to identify characters used to separate words in a line of text, such as the space (‘ ‘) and tab (‘\t’) characters in the standard “C” locale.

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Syntax of isblank()

int isblank(int c);

Parameters

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

This function is standardized in C99 and, in C++11, a locale-specific template version exists. In the standard “C” locale, isblank() considers the tab character ('\t') and the space character (' ') as blank characters.

Return Value

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

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Examples for isblank()

Example 1: Basic Check for a Space Character

This example demonstrates how to check if a single character, specifically a space, is considered blank using isblank().

Program

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

int main() {
    int ch = ' ';
    
    if (isblank(ch)) {
        printf("The character is blank.\n");
    } else {
        printf("The character is not blank.\n");
    }
    
    return 0;
}

Explanation:

1. A character variable is initialized with a space character (' ').
2. The isblank() function checks if this character qualifies as a blank.
3. Since a space is a blank character in the standard “C” locale, the program outputs that the character is blank.

Program Output:

The character is blank.

Example 2: Checking a Tab Character as Blank

This example shows how the isblank() function identifies a tab character as blank in the standard “C” locale.

Program

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

int main() {
    int ch = '\t';
    
    if (isblank(ch)) {
        printf("The character is a tab and is considered blank.\n");
    } else {
        printf("The character is not considered blank.\n");
    }
    
    return 0;
}

Explanation:

1. A character variable is initialized with the tab character ('\t').
2. The isblank() function checks if the tab is classified as a blank character.
3. In the standard “C” locale, the tab is considered blank, so the program outputs that the character is a tab and is considered blank.

Program Output:

The character is a tab and is considered blank.

Example 3: Scanning a String for Blank Characters

This example checks each character in a string to determine which characters are considered blank using isblank().

Program

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

int main() {
    char text[] = "Hello\t World!";
    int i = 0;
    
    while (text[i] != '\0') {
        if (isblank(text[i])) {
            printf("'%c' is blank.\n", text[i]);
        } else {
            printf("'%c' is not blank.\n", text[i]);
        }
        i++;
    }
    
    return 0;
}

Explanation:

1. A string containing letters, a tab, and a space is defined.
2. The program iterates through each character in the string.
3. The isblank() function checks if each character is a blank.
4. A message is printed for each character indicating whether it is blank or not.

Program Output:

'H' is not blank.
'e' is not blank.
'l' is not blank.
'l' is not blank.
'o' is not blank.
'       ' is blank.
' ' is blank.
'W' is not blank.
'o' is not blank.
'r' is not blank.
'l' is not blank.
'd' is not blank.
'!' is not blank.