在 Makefile 的链接过程中添加库的问题

Posted 2023-02-22

【中文标题】在 Makefile 的链接过程中添加库的问题

【英文标题】：problem in adding libraries during linking process in Makefile

【发布时间】：2019-07-27 08:32:01

【问题描述】：

我是 Makefile 的新手。我在一个项目中使用 opencv 和 lpthread 库。以下 makefile 代码似乎不起作用。似乎链接过程失败了。请指出我在这里犯的错误。

操作系统：Ubuntu 18.04

CC=g++
LIBS=`pkg-config --cflags --libs opencv`
CXXFLAGS= -c -Wall -std=c++17 -lpthread -march=native -mtune=native -O2
CXXFLAGS2= -Wall -std=c++17 -lpthread -march=native -mtune=native -O2
all: a.out

a.out: main.o brain_starter.o brain_class.o segment_class.o \
       logic_core.o data_package_class.o core_class.o 
    $(CC) $(CXXFLAGS2) $(LIBS) -o a.out main.o brain_starter.o brain_class.o \
            segment_class.o logic_core.o data_package_class.o core_class.o

main.o: main.cpp dependency_functions.h
    $(CC) $(CXXFLAGS) main.cpp

brain_starter.o: brain_starter.cpp
    $(CC) $(CXXFLAGS) brain_starter.cpp

brain_class.o: brain_class.cpp
    $(CC) $(CXXFLAGS) brain_class.cpp

segment_class.o: segment_class.cpp
    $(CC) $(CXXFLAGS) segment_class.cpp

logic_class.o: logic_class.cpp
    $(CC) $(CXXFLAGS) logic_class.cpp

data_package_class.o: data_package_class.cpp
    $(CC) $(CXXFLAGS) $(LIBS) data_package_class.cpp

core_class.o: core_class.cpp
    $(CC) $(CXXFLAGS) core_class.cpp

clean:
    rm -rf *o a.out

【参考方案1】：

我重新排列了链接代码中的库并且生成文件正常工作。这是工作代码。

CC=g++
OPENCVLIBS=`pkg-config --cflags --libs opencv`
LIBS= -lpthread
CXXFLAGS= -c -Wall -std=c++17 -march=native -mtune=native -O2
CXXFLAGS2= -Wall -std=c++17 -lpthread -march=native -mtune=native -O2
all: a.out

a.out: main.o brain_starter.o brain_class.o segment_class.o \
       logic_core.o data_package_class.o core_class.o 
    $(CC) $(CXXFLAGS2) -o a.out main.o brain_starter.o brain_class.o segment_class.o logic_core.o data_package_class.o core_class.o $(LIBS) $(OPENCVLIBS)

main.o: main.cpp dependency_functions.h
    $(CC) $(CXXFLAGS) $(LIBS) main.cpp

brain_starter.o: brain_starter.cpp
    $(CC) $(CXXFLAGS) $(LIBS) brain_starter.cpp

brain_class.o: brain_class.cpp
    $(CC) $(CXXFLAGS) $(LIBS) brain_class.cpp

segment_class.o: segment_class.cpp
    $(CC) $(CXXFLAGS) $(LIBS) segment_class.cpp

logic_class.o: logic_class.cpp
    $(CC) $(CXXFLAGS) $(LIBS) logic_class.cpp

data_package_class.o: data_package_class.cpp
    $(CC) $(CXXFLAGS) $(LIBS) $(OPENCVLIBS) data_package_class.cpp

core_class.o: core_class.cpp
    $(CC) $(CXXFLAGS) core_class.cpp

clean:
    rm -rf *o a.out

【讨论】：

是的，目标文件和库在链接命令行上的列出顺序很重要。通常，一个目标文件或库中尚未解析的符号只能由稍后在命令行中列出的对象解析。