Reversing Strings in Standard C

Unlike some high-level languages, standard ISO C does not provide a standard library function like strrev() in standard <string.h> (it was a non-standard MS-DOS/Windows extension). The standard, portable way to reverse a string is using an in-place two-pointer swap algorithm.

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C Code Implementation

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <string.h>

void reverseString(char *str) {
    if (str == NULL) return;

    int left = 0;
    int right = strlen(str) - 1;

    while (left < right) {
        /* Swap characters at left and right indices */
        char temp = str[left];
        str[left] = str[right];
        str[right] = temp;

        left++;
        right--;
    }
}

int main() {
    char greeting[] = "Hello, C Compiler!";
    
    printf("Original String: \"%s\"\n", greeting);
    reverseString(greeting);
    printf("Reversed String: \"%s\"\n", greeting);

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Original String: "Hello, C Compiler!"
Reversed String: "!relipmoC C ,olleH"

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Complexity Analysis

• Time Complexity: O(n) where n is string length (loops $⌊ n/2 ⌋$ times).
• Space Complexity: O(1) in-place character manipulation.

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Related Programs

• Test string symmetry in Palindrome Program in C.
• Master pointers and character buffers in Pointers in C.