i cannot compile enca with libiconv

[yangchao]

i configure enca with command:./configure --with-libiconv=/usr/local/
becase my iconv header in /usr/local/include/iconv.h
and lib in /usr/local/lib/libiconv.so
but this not work error is:
checking for iconv... yes
checking for working iconv... no
checking for iconv declaration...
extern size_t iconv (iconv_t cd, char * *inbuf, size_t *inbytesleft, char * *outbuf, size_t *outbytesleft);
checking whether iconv implementation is usable... no