c++ - makefile 错误

Question

在ubuntu下面写算法，用makefile进行自动编译.

我的目录结构如下：

• graph

  • main.cpp
  • graph.cpp
  • vertex.cpp
  • edge.cpp
  • graph.h
  • vertex.h
  • edge.h

• union_find_set

  • main.cpp
  • union_find.cpp
  • union_find_set.cpp
  • union_find.h
  • union_find_set.h

依赖关系是这样的：

union_find.h引用了graph目录下面的vertex.h graph.cpp 引用了union_find_set目录下面的union_find_set.h.

其他的都是引用各自目录下面的文件了。

我的makefile如下：

union_find_set目录下面的makefile

union_find_set : main.o union_find_set.o union_find.o
    g++ -o union_find_set main.o union_find_set.o union_find.o

main.o : main.cpp union_find_set.h
    g++ -c main.cpp
union_find_set.o : union_find_set.cpp union_find_set.h
    g++ -c union_find_set.cpp

union_find.o : union_find.cpp union_find.h
    g++ -c union_find.cpp

clean:
    rm union_find_set *.o

2. graph目录下面的makefile

#include ../union_find_set/makefile

graph : main.o graph.o edge.o vertex.o
    g++ -o graph main.o graph.o edge.o vertex.o
main.o : main.cpp graph.h
    g++ -c main.cpp
graph.o : graph.cpp graph.h ../union_find_set/union_find_set.h
    g++ -c graph.cpp

edge.o : edge.cpp edge.h
    g++ -c edge.cpp

vertex.o : vertex.cpp vertex.h
    g++ -c vertex.cpp

clean :
    rm graph *.o

最后编译出现如下错误：

g++ -o graph main.o graph.o edge.o vertex.o graph.o: In function Graph::Kruskal()': graph.cpp:(.text+0x1328): undefined reference toUnionFindSet::UnionFindSet()' graph.cpp:(.text+0x13c4): undefined reference to Node::Node(Node*, int)' graph.cpp:(.text+0x13e3): undefined reference toNode::setData(Vertex)' graph.cpp:(.text+0x13f5): undefined reference to UnionFindSet::addNode(Node*)' graph.cpp:(.text+0x1641): undefined reference toUnionFindSet::findNode(Vertex)' graph.cpp:(.text+0x1656): undefined reference to UnionFindSet::findNode(Vertex*)' graph.cpp:(.text+0x166b): undefined reference toUnionFindSet::findSet(Node)' graph.cpp:(.text+0x167f): undefined reference to UnionFindSet::findSet(Node*)' graph.cpp:(.text+0x16bb): undefined reference toUnionFindSet::merge(Node, Node*)' collect2: ld returned 1 exit status make: *** [graph] Error 1

这几个函数都是union_find_set.h中定义的函数，在graph.cpp中的kruskal函数中用到，请问我的makefile错在哪里啊 多谢了

Answer 1

The functions declared in union_find_set.h cannot be found during linking. You should define these functions in union_find_set.cpp
Therefore, union_find_set.o should be added when generating the graph. That is

graph : main.o graph.o edge.o vertex.o  
    g++ -o graph main.o graph.o edge.o vertex.o

changed to

graph : main.o graph.o edge.o vertex.o union_find_set.o  
    g++ -o graph main.o graph.o edge.o vertex.o union_find_set.o  

In this way, the previously undefined reference to XXX will be found in union_find_set.o when linking