c - GCC looks for headers in /usr/local/include when compiling, but not for libraries in /usr/local/lib when linking. Why? -

i have installed in /usr/ distribution provided version of sqlite - version 3.4.2. have installed in /usr/local/ sqlite version 3.7.4.

/usr/include/sqlite3.h defines sqlite_version_number 3004002
/usr/local/include/sqlite3.h defines sqlite_version_number 3007004

version 3007004 has function sqlite3_initialize(), version 3004002 not.

$ nm -d /usr/local/lib/libsqlite3.so | grep sqlite3_initialize 00018e20 t sqlite3_initialize 

when compile following example program:

#include <stdio.h> #include <sqlite3.h>  // should fail if including /usr/include/sqlite3.h #if sqlite_version_number != 3007004     #error "sqlite version not 3.7.4" #endif  int main() {     printf( "%d\n", sqlite_version_number );     sqlite3_initialize();     return 0; } 

when compiled , linked (with gcc 4.2.4) preprocessor finds sqlite3.h header version 3.7.4 in /usr/local/include/, linker fails it's looking in /usr/lib/libsqlite3.so symbols.

$ gcc -wall test.c -o cpp -lsqlite3 /tmp/cc4issn6.o: in function `main': test.c:(.text+0x26): undefined reference `sqlite3_initialize' test.c:(.text+0x2b): undefined reference `sqlite3_shutdown' collect2: ld returned 1 exit status 

of course can specify lib directory , links correct version of library.

$ gcc -wall test.c -o cpp -l/usr/local/lib -lsqlite3 $ ./cpp 3007004 $ 

it seems default gcc looks in /usr/local/include/ before /usr/include/ headers, not libraries when linking. why?

edit 1: suggested tim post:

$ sudo ldconfig -n /usr/local/lib $ ldconfig -p | grep sqlite3     libsqlite3.so.0 (libc6) => /usr/local/lib/libsqlite3.so.0     libsqlite3.so.0 (libc6) => /usr/lib/libsqlite3.so.0     libsqlite3.so (libc6) => /usr/local/lib/libsqlite3.so     libsqlite3.so (libc6) => /usr/lib/libsqlite3.so $ gcc -wall cpp.c -o cpp -lsqlite3 /tmp/ccwpt9o0.o: in function `main': cpp.c:(.text+0x26): undefined reference `sqlite3_initialize' cpp.c:(.text+0x2b): undefined reference `sqlite3_shutdown' collect2: ld returned 1 exit status 

the include file search path defined gcc, library search path encoded ld, separate project; these not synchronized.

one thing patch specs file, which, if exists, can found in same directory libgcc; can path latter using

gcc -print-libgcc-file-name 

if there no specs file there, create 1 using

gcc -dumpspecs >specs 

and verify gcc reading it, calling

gcc -v 

look line containing %{l*}, , add -l/usr/local/lib behind (separated spaces). gcc pass argument following -l options command line ld when linking.

in order restore defaults, revert specs file initial state (i.e. delete if didn't exist before).