online_distribution/newbasic/strnstr.cc

0001 /*
0002
0003 This function is modelled after the "strstr" function in
0004 string.h. There is no standard function which locates a substring in a
0005 string which is not 0-terminated. In all other respects the strnstr
0006 function is suuposed to behave as strstr, that is, it returns a
0007 pointer to the first occurence of string s2 in string s1, only that we
0008 can deal here without not 0-terminated strings and rather tell the
0009 length of the strings by the s1len and s2len parameters.
0010
0011 On some systems the memmem function does this, but it is not available on
0012 all systems.
0013
0014 */
0015 #include <iostream>
0016 #include <cstring>
0017
0018 char * strnstr (const char *s1, size_t s1len, const char *s2, size_t s2len)
0019 {
0020
0021   size_t i;
0022   char *c;
0023
0024   /* if s2len is 0, we are done */
0025   if (s2len <= 0) return (char *) s1;
0026
0027   /* if s2len > s1len we will not find the substring here. */
0028   if (s2len > s1len ) return 0;
0029
0030   char *s2copy = new char[s2len+1];
0031   c = s2copy;
0032   for (i=0; i<s2len; i++) *c++ = s2[i];
0033   *c = 0;
0034
0035   c = (char *) s1;
0036   for (i=0; i <= s1len - s2len; i++)
0037     {
0038       if (strncmp(c, s2copy, s2len) == 0)
0039     {
0040       delete [] s2copy;
0041       return c;
0042     }
0043       c++;
0044     }
0045   delete [] s2copy;
0046   return 0;
0047 }
0048