Void-valued Function to extract substring from a string

I need help in writing a a void-valued function to extract a substring from an existing string.

For Example:
     char   sub[80];
     ...
     substr ('Converting to C', 7, 4, &sub);

would store the string 'ting' into the variable called 'sub'. The function should store a NUL character at the end of the extracted string.
LVL 2
cyraxAsked:
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linpageCommented:
the following will do it.  However most 'c' programmers would probably make your example substr('Converting to C', 6, 4, &sub);   because of the 0 offset convention (change the line to while ( *src && start-- > 0) for this).  This snippet tests for the
src running out, but not the destination buffer.  You might want
to include a length for dest to be on the safe side.

void substr(const char* src, int start, int len, char ** dest)
{
  while ( *src && --start > 0)
      src++;
 
  while ( *src && len > 0)
  {
    **dest = *src;
    *dest++;
    src++;
    len--;
  }
  **dest = 0x00;
}
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