我想学习如何用C ++制作共享库。因此,我找到了一些生成Mandelbrot PPM图像的逻辑,并将其封装在src/mandelbrot.cpp
中(并附带了头文件include/mandelbrot.cpp
)。目录树如下所示:
$ tree
.
├── Makefile
├── include
│ └── mandelbrot.h
├── lib
│ └── mandelbrot.dylib
└── src
├── client.cpp
├── main
├── main.cpp
├── mandelbrot.cpp
└── mandelbrot.o
[目标是src/client.cpp
使用lib/mandelbrot.dylib
绘制分形而无需访问src/mandelbrot.cpp
或src/mandelbrot.o
。
Makefile:
.PHONY=clean
main: src/mandelbrot.o
clang++ src/main.cpp -o src/main src/mandelbrot.o -I ./include
src/mandelbrot.o:
clang++ -c src/mandelbrot.cpp -o src/mandelbrot.o -I ./include
clean:
rm src/*.o
rm lib/*.dylib
lib/mandelbrot.dylib:
clang++ -dynamiclib -o lib/mandelbrot.dylib src/mandelbrot.cpp -I ./include
src/client: lib/mandelbrot.dylib
clang++ src/client.cpp -o src/client -L ./lib -I ./include
在没有dylib的情况下运行可执行文件:
$ make main
clang++ src/main.cpp -o src/main src/mandelbrot.o -I ./include
$ ./src/main # runs fine!
但是编译src/client.cpp
时无法链接共享库:
$ make src/client
clang++ src/client.cpp -o src/client -L ./lib -I ./include
Undefined symbols for architecture x86_64:
"fractal::Mandelbrot::writeToFile(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >)", referenced from:
_main in client-e344c7.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [src/client] Error 1
即使该符号似乎在dylib中:
$ file lib/mandelbrot.dylib
lib/mandelbrot.dylib: Mach-O 64-bit dynamically linked shared library x86_64
$ nm -C lib/mandelbrot.dylib | grep writeToFile
0000000000001460 T fractal::Mandelbrot::writeToFile(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >)
我正在尝试更深入地了解链接/编译过程。如何进行我要进行的设置以演示我想做什么?
尝试像libmandelbrot.dylib这样命名您的库以匹配-lmandelbrot标志
贷方@Daniel寻求答案,但略述原因。
我可以通过重命名mandelbrot.dylib
-> libmandelbrot.dylib
使编译工作,如@daniel的答案所建议。
我研究了man ld
(链接器),发现以下定义:
-lx This option tells the linker to search for libx.dylib or libx.a in the library search path. If string x is of the form y.o, then that file is searched for in the same places, but without prepending
`lib' or appending `.a' or `.dylib' to the filename.
因此,如果要随意命名动态加载的库(由于某种原因,不喜欢在名称前加上libxxxx的魔力,那么您就必须这样做(我已经证实了这是可行的:]
lib/whatever.o:
clang++ -dynamiclib -o lib/whatever.o src/mandelbrot.cpp -I ./include
src/client: lib/whatever.o
clang++ src/client.cpp -o src/client -L ./lib -I ./include -l whatever.o
TL; DR =通过将-l
选项作为以.o
结尾的文件名,链接器直接在-L
指定的目录中查找-l
中指定的确切文件名。否则-l foo -L /path/
搜索/path/libfoo.[dylib|a]