Returns the portion of str specified by the start and length parameters.
If start is non-negative, iconv_substr() cuts the portion out of str beginning at start'th character, counting from zero.
If start is negative, iconv_substr() cuts out the portion beginning at the position, start characters away from the end of str.
If length is given and is positive, the return value will contain at most length characters of the portion that begins at start (depending on the length of string). If str is shorter than start characters long, FALSE will be returned.
If negative length is passed, iconv_substr() cuts the portion out of str from the start'th character up to the character that is length characters away from the end of the string. In case start is also negative, the start position is calculated beforehand according to the rule explained above.
Note that offset and length parameters are always deemed to represent offsets that are calculated on the basis of the character set determined by charset, whilst the counterpart substr() always takes these for byte offsets. If charset is not given, the character set is determined by the iconv.internal_charset ini setting.