AC_CHECK_LIB

[Bob Lockie]

checking for deflate in -lz... yes
checking for ID3Tag_Link in -lid3... no

AC_CHECK_LIB adds the "-l" some of the time but does it not in the case 
of "libz"?

$ autoconf --version
autoconf (GNU Autoconf) 2.57

:config.log:
------------
configure:30486: checking for deflate in -lz
configure:30517: gcc -o conftest -ansi -W -Wall -pedantic 
-Wchar-subscripts -Ws
hadow -Wpointer-arith -Wmissing-prototypes -Wwrite-strings 
-D_XOPEN_SOURCE=500
-D_BSD_SOURCE -O2  -ansi -W -Wall -pedantic -Wchar-subscripts -Wshadow 
-Wpointe
r-arith -Wmissing-prototypes -Wwrite-strings -D_XOPEN_SOURCE=500 
-D_BSD_SOURCE
-O2   -Wformat-security -Wmissing-format-attribute -Wformat-security 
-Wmissing-
format-attribute  -DQT_THREAD_SUPPORT  -D_REENTRANT  conftest.c -lz 
-lvorbisfi
le -lvorbis -lstdc++  >&5
configure:30520: $? = 0
configure:30523: test -s conftest
configure:30526: $? = 0
configure:30538: result: yes
configure:30549: checking for ID3Tag_Link in -lid3
configure:30580: gcc -o conftest -ansi -W -Wall -pedantic 
-Wchar-subscripts -Ws
hadow -Wpointer-arith -Wmissing-prototypes -Wwrite-strings 
-D_XOPEN_SOURCE=500
-D_BSD_SOURCE -O2  -ansi -W -Wall -pedantic -Wchar-subscripts -Wshadow 
-Wpointe
r-arith -Wmissing-prototypes -Wwrite-strings -D_XOPEN_SOURCE=500 
-D_BSD_SOURCE
-O2   -Wformat-security -Wmissing-format-attribute -Wformat-security 
-Wmissing-
format-attribute  -DQT_THREAD_SUPPORT  -D_REENTRANT  conftest.c -lid3 
-lvorbis
file -lvorbis -lstdc++  >&5
/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3/../../../libid3.so: undefined 
reference to `uncompress'
/usr/lib/gcc-lib/i686-pc-linux-gnu/3.2.3/../../../libid3.so: undefined 
reference to `compress'
collect2: ld returned 1 exit status


:snippit of my configure.in:
----------------------------
dnl id3lib library (required)
    AC_CHECK_LIB( [z], [deflate],
                  configure_enable_id3lib="yes",
                  configure_enable_id3lib="no", )

    if test "x$configure_enable_id3lib" = "xyes"; then
        AC_CHECK_LIB( id3, ID3Tag_Link,, configure_enable_id3lib="no", )
    fi