Question

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Reversing a string in C

I’m currently switching from C++ to C programming for a project and I haven’t done much with Char arrays as strings. I need a function that will read in a pointer to a char array and reverse it. I wrote this in C++, which is pretty easy using the string functions, but I’m a little confused on if there are functions or something else in C that is the best way to do this. Thanks, and I’m not necessarily looking for someone to completely finish the code, but to point me in the right direction. If it’s simple one line something feel free, but don’t do anything that makes you feel uncomfortable.

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

void reverseString(char *myString)
{
    //reverse string here
}

int main(void)
{
    char myString[] = "This is my string!";
    reverseString(myString);

    return 0;
}

Answer 1

Simplest way: Loop the string char by char and insert each char to another char array in the reverse order.

Or try this:
2)

void reverse_string(char str[])
{
    char c;
    char *p, *q;

    p = str;
    if (!p)
        return;

    q = p + 1;
    if (*q == '\0')
        return;

    c = *p;
    reverse_string(q);

    while (*q != '\0') {
        *p = *q;
        p++;
        q++;
    }
    *p = c;

    return;
}

3)

if( strlen( str ) > 0 ) {
   char* first = &str[ 0 ];
   char* last = &str[ strlen( str ) - 1 ];
   while( first < last ) {
       char tmp = *first;
       *first = *last;
       *last = tmp;
      ++first;
      --last;

4)

char* strrev( char* s )
  {
  char  c;
  char* s0 = s - 1;
  char* s1 = s;

  /* Find the end of the string */
  while (*s1) ++s1;

  /* Reverse it */
  while (s1-- > ++s0)
    {
    c   = *s0;
    *s0 = *s1;
    *s1 =  c;
    }

  return s;
  }