C Program to Trim Leading Whitespaces from String

Trimming leading white spaces from a string means removing any unnecessary spaces before the first non-space character in the string. In this article, we will learn how to trim leading white spaces using the C program.

The most straightforward method to trim leading white spaces from the string is by using a two-pointer approach. Let’s take a look at an example:

#include <stdio.h>

void trim(char *s) {
  
  	// Two pointers initially at the beginning
    int i = 0, j = 0;

    // Skip leading spaces
    while (s[i] == ' ') i++; 

    // Shift the characters of string to remove
  	// leading spaces
    while (s[j++] = s[i++]);
}

int main() {
    char s[] = "   Hello, Geeks!";
  
  	// Remove leading whitespaces from s
    trim(s);  

    printf("'%s'\n", s);
    return 0;
}

'Hello, Geeks!'

Explanation: The above program uses two pointers: i finds the first non-space character, while j copies subsequent characters to the beginning of the string, effectively removing the leading spaces. Finally, it null-terminates the trimmed string.

There are also some other ways to remove the leading whitespace from a string in C. Some of them are given below:

Using Pointer Arithmetic

Instead of using array indexing, we can use pointer arithmetic to traverse the string. We move the pointer to the first non-space character and then shift the string to remove the leading spaces.

#include <stdio.h>
#include <string.h>

void trim(char *s) {
  
    // Pointer to the beginning of the trimmed string
    char *ptr = s;

    // Skip leading spaces
    while (*s == ' ') s++;

    // Shift remaining characters to the beginning
    while (*ptr++ = *s++);
}

int main() {
    char s[] = "  Hello, Geeks!";
  
  	// Remove leading whitespaces from s
    trim(s);
  
    printf("%s\n", s);
    return 0;
}

'Hello, Geeks!'