Linked cannot find symbols, but libraries are read and symbols exist

问题

I've been trying to compile my project and I'm getting undefined reference errors. eg.:

installertest.cpp:(.text+0x9d1): undefined reference to `XmlRpcValue::makeArray()'
...
installertest.cpp:(.text+0xede): undefined reference to `dbcancel'
installertest.cpp:(.text+0xefd): undefined reference to `dbfcmd'
installertest.cpp:(.text+0xf0f): undefined reference to `dbsqlexec'
installertest.cpp:(.text+0xf2d): undefined reference to `SHA1_Init'
...

My command-line is:

g++ -o installertest \
    -lsybdb \
    -lxmlrpc \
    -lxmlrpc_cpp \
    -lxmlrpc_xmlparse \
    -lxmlrpc_xmltok \
    -lxmlrpc_util \
    -lxmlrpc++ \
    -lxmlrpc_server_cgi \
    -lssl \
    -std=c++0x \
    ContractData.o installertest.o

objdump -T shows that the symbols are in the .so file. eg.:

libsybdb.so:
...
0000000000011c30 g    DF .text  0000000000000083  Base        dbcancel
...

/usr/lib/libxmlrpc_cpp.so:
...
0000000000002e78 g    DF .text  0000000000000092  Base        _ZN11XmlRpcValue9makeArrayEv
...

strace shows that the library files are being opened and read by the linker:

...
[pid  5019] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libsybdb.so", {st_mode=S_IFREG|0644, st_size=421608, ...}) = 0
[pid  5019] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libsybdb.so", O_RDONLY) = 7
[pid  5019] fcntl(7, F_GETFD)           = 0
[pid  5019] fcntl(7, F_SETFD, FD_CLOEXEC) = 0
[pid  5019] fstat(7, {st_mode=S_IFREG|0644, st_size=421608, ...}) = 0
[pid  5019] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2b16c200c000
[pid  5019] lseek(7, 0, SEEK_SET)       = 0
[pid  5019] read(7, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\237\0\0\0\0\0\0"..., 4096) = 4096
...
[pid  5019] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libxmlrpc.so", {st_mode=S_IFREG|0644, st_size=80936, ...}) = 0
[pid  5019] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libxmlrpc.so", O_RDONLY) = 8
[pid  5019] fcntl(8, F_GETFD)           = 0
[pid  5019] fcntl(8, F_SETFD, FD_CLOEXEC) = 0
[pid  5019] fstat(8, {st_mode=S_IFREG|0644, st_size=80936, ...}) = 0
[pid  5019] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2b16c200d000
[pid  5019] lseek(8, 0, SEEK_SET)       = 0
[pid  5019] read(8, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300?\0\0\0\0\0\0"..., 4096) = 4096
...

All files involved are targeted to x86-64 and the header for the C libraries are extern "C". I have tried everything I can think of and it still won't link.

I've even tried removing all C++11 code and compiling without the command-line switch, still nothing.

My system is Ubuntu Precise (12.04) 64-bit using g++ (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3 if that helps. All packages were installed from the package manager and development packages are installed.

Edit (2017-05-30): Marked as duplicate of https://stackoverflow.com/questions/45135/why-does-the-order-in-which-libraries-are-linked-sometimes-cause-errors-in-gcc
Other question asks why order of arguments is important. Argument order was not known to be an issue when question was asked.
Also, previous question does not contain any helpful expansion, whereas this question shows the issue at hand.
Previous question may be seen as a helpful expansion on the answer to this one, but not a duplication.

回答1:

You have to put the libraries' linker flags after the object files. So, instead of

g++ -o installertest \
-lsybdb \
-lxmlrpc \
-lxmlrpc_cpp \
-lxmlrpc_xmlparse \
-lxmlrpc_xmltok \
-lxmlrpc_util \
-lxmlrpc++ \
-lxmlrpc_server_cgi \
-lssl \
-std=c++0x \
ContractData.o installertest.o

use

g++ -o installertest \
ContractData.o installertest.o \
-lsybdb \
-lxmlrpc \
-lxmlrpc_cpp \
-lxmlrpc_xmlparse \
-lxmlrpc_xmltok \
-lxmlrpc_util \
-lxmlrpc++ \
-lxmlrpc_server_cgi \
-lssl \
-std=c++0x

来源：https://stackoverflow.com/questions/11112318/linked-cannot-find-symbols-but-libraries-are-read-and-symbols-exist

标签

Linux

g++

shared-objects