Question

我有一个包含以下文件的项目，所有项目都在同一个文件夹中

client.c
server.c
reliable_udp.h
reliable_udp.c
conf.h

在其他库中，client.c还包括reliable_udp.h（#include "reliable_udp.h"），以便使用packet_send和print_conf函数（在reliable_udp.c中实现{1}}）。

我是Makefile的新手，我试图写一个：

CC = gcc
CFLAGS = -Wall -Wextra -Wpedantic -O3
SRC = client.c server.c
OBJ = $(SRC:.c=.o)

all: $(OBJ)
        ${CC} ${CLFAGS} client.o -o client
        ${CC} ${CLFAGS} server.o -o server

client.o: reliable_udp.h

clean:
        rm -f *.o core

cleanall:
        rm -f *.o core client server

如果我尝试运行make，我会得到以下输出：

gcc -Wall -Wextra -Wpedantic -O3   -c -o client.o client.c
gcc  client.o -o client
client.o: In function `main':
client.c:(.text.startup+0x84): undefined reference to `packet_send'
client.c:(.text.startup+0x8b): undefined reference to `print_conf'
collect2: error: ld returned 1 exit status
Makefile:7: recipe for target 'all' failed
make: *** [all] Error 1

显然我没有正确地写Makefile。我该如何解决？ 为什么我收到此错误？

Answer 1

快速解决方法是修改Makefile，如下所示：

all: $(OBJ)
        ${CC} ${CLFAGS} reliable_udp.o client.o -o client
        ${CC} ${CLFAGS} reliable_udp.o server.o -o server

它并不漂亮，在现实世界中＃34;一个更好的选择可能是为＆＃34; reliable_udp＆＃34;创建一个共享库，或者至少重构一下Makefile。

错误的原因是＆＃34; reliable_udp＆＃34;未编译到最终的二进制文件中，因为它未在makefile中的任何位置显式指定。

Answer 2

为什么我收到此错误？

因为链接配方不包含'reliable_udp.0'对象，并且因为makefile中的任何内容都不会将'reliable_udp.c'编译为'reliable_udp.o`

发布的makefile包含几个问题，如问题评论中所述。

以下是一个提议的简单makefile，它应该执行所需的功能。

注意：将<tab>替换为制表符

注意：在以下makefile中，调用命令可以是：

make          -- to generate both 'client' and 'server'
                 as it will use the first target, which is 'all'
make all      -- to generate both 'client' and 'server'
make client   -- to only generate the 'client' executable
make server   -- to only generate the 'server' executable
make clean    -- to delete the object files
make cleanall -- to delete the object files and the executables

现在提出的makefile

#use ':=' rather than '=' so macros only evaluated once

#assure the desired utilities are used
CC := /usr/bin/gcc
RM := /usr/bin/rm -f

CFLAGS := -Wall -Wextra -Wpedantic -std=GNU11 -O3

#generate a list of all the source files
SRC := client.c server.c reliable_udp.c

#generate a list of all the object file names
OBJ := $(SRC:.c=.o)

#let make know that the target 'all' will not produce a file of the same name
#notice the 'all' target dependencies are the final executables
.PHONY: all
all: client server

#this will perform all the compiles
#while expecting the user supplied header files to be in the local directory
%.o:%.c
<tab>$(CC) -c $(CFLAGS) $^ -o $@ -I.

#link the 'client' executable
client: client.o reliable_udp.o
<tab>${CC}  $^ -o $@

#link the 'server' executable
server: server.o reliable_udp.o
<tab>${CC}  $^ -o $@

#let make know that this target will not produce a file of the same name
.PHONY: clean
clean:
<tab>$(RM) $(OBJ) core

#let make know that this target will not produce a file of the same name
.PHONY: cleanall
cleanall:
<tab>$(RM) $(OBJ) core client server

将头文件与makefile链接：未定义的引用错误

2 个答案: