C Program to Reverse Strings on Command Line

On command line, we want to reverse the parameters, we can compile the following C program to produce a exectuable.

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

void reverse(char *buf, int i, int j) {
    while (i < j) {
        char t = buf[i];
        buf[i] = buf[j];
        buf[j] = t;
        i ++;
        j --;
    }
}

int main(int argc, char* argv[]) {
    if (argc == 0) {
        return 0;
    }
    for (int i = 1; i < argc; ++ i) {
        int l = strlen(argv[i]);
        reverse(argv[i], 0, l - 1);
        printf("%s\n", argv[i]);
    }
    return 0;
}

To reverse a string is easy – we can use the two pointer to swap the characters at both pointer and move them towards each other until they meet in the middle.

To compile the above C code:

$ gcc reverse.c -o rev

Example usage:

$ ./rev abc
cba
$ ./rev abc def
cba
fed
$ ./rev "123 456"
654 321

As you see, we can reverse each parameters, or we can reverse all by wrapping parameters in a quote.

–EOF (The Ultimate Computing & Technology Blog) —