Is there a reverse function for strstr

Question

I am trying to find a similar function to strstr that searches a substring starting from the end towards the beginning of the string.

Answer 1

Long story short:

Nope - there is no function in the C-library that does what you need..

But as others have pointed out: It's not rocket-science to write such a function...

Answer 2

One possible, if not entirely elegant, implementation might look like:

#include "string.h"

const char* rstrstr(const char* haystack, const char* needle)
{
  int needle_length = strlen(needle);
  const char* haystack_end = haystack + strlen(haystack) - needle_length;
  const char* p;
  size_t i;

  for(p = haystack_end; p >= haystack; --p)
  {
    for(i = 0; i < needle_length; ++i) {
      if(p[i] != needle[i])
        goto next;
    }
    return p;

    next:;
  }
  return 0;
}

Answer 3

Though non-standard, strrstr is widely supported and does exactly what you want.

Answer 4

char * strrstr(char *_Str, char *_SubStr){
    char *returnPointer, *p;

    //find 1st occurence. if not found, return NULL
    if ( (p=strstr(_Str, _SubStr))==NULL)
        return NULL;

    //loop around until no more occurences
    do{
        returnPointer=p;
        ++p;
    }while(p=strstr(p, _SubStr));

    return returnPointer;
}

Answer 5

You can use standard algorithm std::find_end for this purpose. For example

    char s[] = "What is the last word last";
    char t[] = "last";

    std::cout << std::find_end( s, s + sizeof( s ) - 1, t, t + sizeof( t ) -1 )
              << std::endl;