g ++静态库的顺序很重要？

Question

我一整天都在努力解决这个问题.我在我的项目中使用了一些库,我总是抱怨一些编译错误undefined reference.

相关文件如下:

encode.cc//the main file
url_codec.h//the header of the libraries, got some function definition in it
libimageenc.a
libmbpicenc.a
liburlaes.a
liburldecode.a

makefile如下:

cflags = -Wall -O2 -fPIC

libpath=./libs/
libs+=$(libpath)liburlaes.a
libs+=$(libpath)liburldecode.a $(libpath)libimageenc.a $(libpath)libmbpicenc.a

cxx  = g++
bin  = encode

all: $(bin)

srcs = $(shell ls *.cc *.cpp)
objs = $(srcs:%.cc=%.o)

$(bin):${objs}
    $(cxx) $(cflags) $(inc) -o $@ ${objs} ${libs}

$(objs):%.o:%.cc
    $(cxx) $(cflags) $(inc) -c -o $@ $<

clean:
    rm -f *.o
    rm -f *.bak
    rm -f $(bin)

g ++编译器抱怨说:

g++ -Wall -O2 -fPIC  -o encode encode.o ./libs/liburlaes.a ./libs/liburldecode.a ./libs/libimageenc.a ./libs/libmbpicenc.a
./libs/liburldecode.a(url_codec.o): In function `url_codec::offpic_url_decode_func(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, int&)':
url_codec.cc:(.text+0x18da): undefined reference to `uuid_unparse'
./libs/liburldecode.a(crypto_aes.o): In function `encode_aes':
crypto_aes.cc:(.text+0x4e): undefined reference to `AES_cbc_encrypt'
./libs/liburldecode.a(crypto_aes.o): In function `decode_aes':
crypto_aes.cc:(.text+0xae): undefined reference to `AES_cbc_encrypt'
./libs/liburldecode.a(crypto_aes.o): In function `init_aes_encrypt_key':
crypto_aes.cc:(.text+0xf3): undefined reference to `AES_set_encrypt_key'
./libs/liburldecode.a(crypto_aes.o): In function `init_aes_decrypt_key':
crypto_aes.cc:(.text+0x143): undefined reference to `AES_set_decrypt_key'
collect2: ld returned 1 exit status

但所有这些功能都在liburlaes.a中得到很好的定义,如图所示 nm -C

    nm -C liburlaes.a | grep -i 'aes'
    decode_byaes.o:
         U AES_cbc_encrypt
         U AES_set_decrypt_key
         U AES_set_encrypt_key
00000060 T decode_byaes
00000000 T encode_byaes
00000110 T init_byaes_decrypt_key
000000c0 T init_byaes_encrypt_key
         U decode_byaes
         U encode_byaes
         U init_byaes_decrypt_key
         U init_byaes_encrypt_key

通过移动liburlaes.a到最后,事情不会变得更好libs,输出完全如上所述.libimageenc向后移动会使情况变得更糟,更多符号声称未定义:

libs+=$(libpath)liburldecode.a $(libpath)libimageenc.a $(libpath)libmbpicenc.a
libs+=$(libpath)liburlaes.a

那么,我该如何解决这个问题呢？

更新

我试图把它liburlaes.a放在两边,但它不起作用,我用'**'包装libaray来强调:

g++ -Wall -O2 -fPIC  -o encode encode.o **./libs/liburlaes.a** ./libs/liburldecode.a ./libs/libimageenc.a ./libs/libmbpicenc.a **./libs/liburlaes.a**
./libs/liburldecode.a(url_codec.o): In function `url_codec::offpic_url_decode_func(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned int&, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, int&)':
url_codec.cc:(.text+0x18da): undefined reference to `uuid_unparse'
./libs/liburldecode.a(crypto_aes.o): In function `encode_aes':
crypto_aes.cc:(.text+0x4e): undefined reference to `AES_cbc_encrypt'
./libs/liburldecode.a(crypto_aes.o): In function `decode_aes':
crypto_aes.cc:(.text+0xae): undefined reference to `AES_cbc_encrypt'
./libs/liburldecode.a(crypto_aes.o): In function `init_aes_encrypt_key':
crypto_aes.cc:(.text+0xf3): undefined reference to `AES_set_encrypt_key'
./libs/liburldecode.a(crypto_aes.o): In function `init_aes_decrypt_key':
crypto_aes.cc:(.text+0x143): undefined reference to `AES_set_decrypt_key'
collect2: ld returned 1 exit status
make: *** [encode] Error 1

Answer 1

是的,图书馆的顺序绝对重要.你需要首先使用库,然后是库.

我遇到过库A依赖库B中的东西,库B需要库A中的东西的情况,所以你需要将库A放在列表中两次.

链接器的工作方式是处理目标文件,然后读取库以解析目标文件中不存在的符号.如果库具有解决依赖关系的对象"文件",则包含这些部分.然后它继续下一个库.它不会"记住"它在之前的库中看到的内容.