strrev() and Portable String Reversal in C

strrev() is a commonly seen compiler extension for reversing a string, but it is not part of the ISO C standard library. Portable C code should reverse the characters directly or use a small helper function.

Legacy Syntax Top ↑

strrev(string);  // non-standard extension

Portable String-Reversal Function Top ↑

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

void reverse_string(char text[]) {
    size_t left = 0;
    size_t right = strlen(text);

    if (right == 0) {
        return;
    }

    right--;

    while (left < right) {
        char temp = text[left];
        text[left] = text[right];
        text[right] = temp;
        left++;
        right--;
    }
}

int main(void) {
    char text[] = "plus2net";

    reverse_string(text);
    printf("%s\n", text);

    return 0;
}

Output

ten2sulp

Reverse User Input Top ↑

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

void reverse_string(char text[]) {
    size_t left = 0;
    size_t right = strlen(text);

    if (right == 0) {
        return;
    }

    right--;

    while (left < right) {
        char temp = text[left];
        text[left] = text[right];
        text[right] = temp;
        left++;
        right--;
    }
}

int main(void) {
    char text[80];

    printf("Enter a string: ");
    if (fgets(text, sizeof text, stdin) == NULL) {
        return 1;
    }

    text[strcspn(text, "\n")] = '\0';
    reverse_string(text);

    printf("Reversed: %s\n", text);
    return 0;
}

Reverse Several Strings Top ↑

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

void reverse_string(char text[]) {
    size_t left = 0;
    size_t right = strlen(text);

    if (right == 0) {
        return;
    }

    right--;

    while (left < right) {
        char temp = text[left];
        text[left] = text[right];
        text[right] = temp;
        left++;
        right--;
    }
}

int main(void) {
    char words[][20] = {"plus2net", "hello", "world"};

    for (size_t i = 0; i < 3; i++) {
        reverse_string(words[i]);
        printf("%s\n", words[i]);
    }

    return 0;
}

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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