makefile错误:对main的未定义引用 [英] makefile error: undefined reference to main

问题描述

我正在尝试使用make来编译我的代码.通常我会这样编译我的代码:

I am trying to compile my piece of code using make. Normally I compile my code like this:

mipsisa32r2el-timesys-linux-gnu-g++ -o testing -I/usr/include/libxml2 -L/develop/xc4/rootfs/parsecpp/lib -L/develop/xc4/rootfs/parsecpp/sqlite-mips2/lib -I/develop/xc4/rootfs/parsecpp/sqlite-mips2/include db.cpp main.cpp networkinterfacemodule.cpp network.cpp multiplex.cpp program.cpp service.cpp -lsqlite3 -lxml2

为了摆脱这个长命令，我尝试编写一个makefile:

To get rid of this long command I tried to write a makefile:

CC= mipsisa32r2el-timesys-linux-gnu-g++

export LD_LIBRARY_PATH=:/parsecpp/sqlite-mips2/lib:/parsecpp/lib:/tmp/vixs_temp/DirectFB/single_core/lib


CFLAGS=-I/usr/include/libxml2 -I/develop/xc4/rootfs/parsecpp/sqlite-mips2/include

LDFLAGS=-L/develop/xc4/rootfs/parsecpp/lib -L/develop/xc4/rootfs/parsecpp/sqlite-mips2/lib

LIBS = -lsqlite3 -lxml2

PROG=testing

all: main.o db.o mod.o multiplex.o network.o networkinterfacemodule.o program.o service.o
    $(CC) -o $(PROG) $(CFLAGS) $(LDFLAGS)  main.o db.o mod.o multiplex.o network.o networkinterfacemodule.o program.o service.o $(LIBS) 

main.o: main.cpp 
    $(CC) $(CFLAGS) $(LDFLAGS) main.cpp db.cpp networkinterfacemodule.cpp mod.cpp multiplex.cpp network.cpp program.cpp service.cpp $(LIBS)

db.o: db.cpp 
    $(CC) $(CFLAGS) $(LDFLAGS) db.cpp $(LIBS)


mod.o: mod.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) mod.cpp $(LIBS)

multiplex.o: multiplex.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) multiplex.cpp $(LIBS)

network.o: network.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) network.cpp $(LIBS)

networkmoduleinterface.o: networkinterfacemodule.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) networkinterfacemodule.cpp $(LIBS)

program.o: program.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) program.cpp $(LIBS)

service.o: service.cpp
    $(CC) $(CFLAGS) $(LDFLAGS) service.cpp $(LIBS)

clean:
    rm -rf *o testing

然后我收到此错误:

/opt/timesys/linux-gnu/toolchain/bin/../../toolchain/lib/crt1.o: In function `__start':
(.text+0xc): undefined reference to `main'
/opt/timesys/linux-gnu/toolchain/bin/../../toolchain/lib/crt1.o: In function `__start':
(.text+0x10): undefined reference to `main'
collect2: ld returned 1 exit status
make: *** [db.o] Error 1

有人可以帮助我吗?

推荐答案

每当您仅编译文件而不链接文件时，请使用"-c"标志.

Whenever you are just compiling a file and not linking it, use the "-c" flag.

例如:-

db.o: db.cpp 
$(CC) -c $(CFLAGS) $(LDFLAGS) db.cpp $(LIBS)

此外，在编译时，不需要向编译器提供"$(LIBS)"，仅在链接时提供它们.您也不需要链接器标志，因为使用"-c"标志时不会调用链接器.

Also, while compiling, there's no need to provide "$(LIBS)" to the compiler, only provide them when linking. Nor do you need the linker flags since linker is not called when using the "-c" flag.

所以你可以写

 db.o: db.cpp 
 $(CC) -c $(CFLAGS) db.cpp

---

已更新(基于评论):-

---

UPDATED (based on comments):-

链接文件时，链接器期望只有一个main功能.在上述情况下，主函数未在db.cpp中定义，因此尽管编译成功，但链接器由于找不到main函数而引发了错误.

When linking the files, the linker expects one and only one main function. In the above case, the main function is not defined in db.cpp and hence although compilation succeeds, the linker throws an error as it cannot find the main function.

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