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为什么Make会自动执行cc命令?

makefile gcc c

verpas · 技术社区 · 1 年前

我正在努力学习如何使用Make!所以我有一个简单的Makefile,

all: main other

main: main.c other.o
    gcc main.c -o main
    echo "Compiled main.exe"

other: other.o

other.c:
    touch $@
    echo "int main(){return 0;}" > $@
    echo "Created other.c"

other.o: other.c
    gcc other.c -o other.o
    echo "Compiled other.o"

clean:
    rm -f main.exe other.o other.c

其中除了在执行cc编译命令的末尾之外,所有内容都按预期执行。这是输出(我添加了箭头),

> make all  
touch other.c
echo "int main(){return 0;}" > other.c
echo "Created other.c"
Created other.c
gcc other.c -o other.o
echo "Compiled other.o"
Compiled other.o
gcc main.c -o main
echo "Compiled main.exe"
Compiled main.exe
cc   other.o   -o other     <---
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o: in functio
n `mainCRTStartup':
/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: multiple definition of `mainCRTStartup'
; /usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../crt0.o:/c/S/B/src/msys2-runtime/winsup/cygw
in/crt0.c:20: first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o: in functio
n `mainCRTStartup':
/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: multiple definition of `WinMainCRTStart
up'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../crt0.o:/c/S/B/src/msys2-runtime/winsup/c
ygwin/crt0.c:20: first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crt
beg:(.text+0x50): multiple definition of `__gcc_register_frame'; /usr/lib/gcc/x86_64-pc-m
sys/13.2.0/crtbegin.o:cygming-crtbeg:(.text+0x0): first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crt
beg:(.text+0x70): multiple definition of `__gcc_deregister_frame'; /usr/lib/gcc/x86_64-pc
-msys/13.2.0/crtbegin.o:cygming-crtbeg:(.text+0x20): first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crt
beg:(.data+0x0): multiple definition of `__dso_handle'; /usr/lib/gcc/x86_64-pc-msys/13.2.
0/crtbegin.o:cygming-crtbeg:(.data+0x0): first defined here
collect2: error: ld returned 1 exit status
make: *** [<builtin>: other] Error 1

“<---”所指向的是有问题的线。为什么这会被处决?

2 回复 | 直到 1 年前

Some programmer dude 1 年前

问题是要生成的默认程序 和链接 程序是 cc 。按照规则 other: other.o 你告诉我 make 以生成可执行文件 other 从对象文件 other.o 然后它将使用默认链接器来执行此操作。

这些错误是因为 gcc other.c -o other.o 构建 可执行程序 名为的文件 另外o 。若要生成对象文件,您需要使用 -c 选项

实际上,解决所有问题的简单方法是设置 CC 和 LD 变量,并依赖于隐式规则来构建代码。

这样一个 Makefile 可能看起来像这样:

# Explicitly use gcc as the compiler and linker
CC = gcc
LD = gcc

# The "default" target, because the first target in the makefile
# is what make will use when no target is specified
default: main other

# Build the main executable program from the main.c source
main: main.c

# Build the other executable program from the other.c source
other: other.c

# Create the other.c source file
other.c:
    echo "int main(){return 0;}" > $@

# The clean target isn't for creating a "clean" file, it's phony, fake
.PHONY: clean
clean:
    -rm -f main other other.c

_{[请注意,您需要将缩进转换为制表符]}

9769953 1 年前

为什么Make会自动执行cc命令?

这些都是隐含的规则。

假设您使用的是GNU Make,请进行通读 https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html ,其中说明

链接单个对象文件

n is made automatically from n.o by running the C compiler to
link the program. The precise recipe used is â$(CC) $(LDFLAGS) n.o
$(LOADLIBES) $(LDLIBS)â.

代替 n 通过 other 对于您的案例。)

为了理解上述变量,例如 CC ,另请参阅 the section on implicit variables 。这就是为什么你看到 cc 在那条线上:

科科斯群岛

用于编译C程序的程序;默认抄送。

自 科科斯群岛 变量用于链接部分。