Difficulty: ★ ★ ★ ☆

As you might already know, the C language lacks plenty o’ functions readily available in other programming languages. Many of these functions, or “methods,” deal with strings. Though C includes a few basic string functions in its library, the C Lords have determined that when you need another such function, you must code it yourself.

The topic for this month’s Exercise is to craft a trim() function, which is one of those capabilities present in other programming languages but not directly in C. What this function does is to remove whitespace characters from both ends of a string.

As a reminder, whitespace characters include space, newline, and tab. The POSIX standard also adds form-feed (\f), carriage return (\r), and vertical tab (\v).

Below is a code skeleton to help get you started. This code runs, but it’s missing the trim() function and the statements to call the function and output the trimmed strings.

2026_04_01-Lesson.c

#include <stdio.h>

/*
   put the trim() function here
 */

int main()
{
    char *sample[] = {
        "   one   ",
        "\ttwo\n",
        "",
        "    ",
        "a",
        " x ",
        NULL,
        " \t three \n",
        "four",
        "  five",
        "six    ",
        " seven eight "
    };
    int size,x;

    /* obtain array size */
    size = sizeof(sample)/sizeof(sample[0]);

    /* output trimmed strings */
    for( x=0; x<size; x++ )
    {
        /* output string
           and trimmed string */
    }

    return 0;
}

The skeleton includes an array sample[] that contains a slew of sample strings to trim. The strings represent a variety of possibilities such as an empty string, a string with only spaces, and NULL. These items are included because your trim() function solution must account for everything!

You can see that I don’t prototype the trim() function, so its behavior is truly at your discretion.

Here is sample output from my solution:

'   one   ' => 'one'
'       two
' => 'two'
'' => ''
'    ' => ''
'a' => 'a'
' x ' => 'x'
'(null)' => Bad string
'        three
' => 'three'
'four' => 'four'
'  five' => 'five'
'six    ' => 'six'
' seven eight ' => 'seven eight'

I can think of multiple ways to code a trim() function, but don’t overthink things! As a suggestion, I recommend tackling the problem one step at a time.

Please try this exercise on your own before you peek at my solution, which I’ll post in a week.