c – 为什么这个非常简单的Makefile产生如此多的调试日志记录？

发布时间：2020-12-16 10:34:13 所属栏目：百科来源：网络整理

导读：我正在学习Makefiles并决定写下我的第一个练习.我有一个包含两个文件的目录： Makefile makefile.cpp 这是makefile.cpp(惊喜！)： #include iostreamint main() { std::cout "Hello World!n"; return 0;} 这是Makefile： CC = g++FILES = makefile.cppOUT_E

我正在学习Makefiles并决定写下我的第一个练习.我有一个包含两个文件的目录：

Makefile  makefile.cpp

这是makefile.cpp(惊喜！)：

#include <iostream>

int main() {
  std::cout << "Hello World!n";
  return 0;
}

这是Makefile：

CC = g++
FILES = makefile.cpp
OUT_EXE = makefileout

build: $(FILES)
    $(CC) -o $(OUT_EXE) $(FILES)

然后我运行make -d并得到一个很长的日志：

$make -d
GNU Make 3.81
Copyright (C) 2006  Free Software Foundation,Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

This program built for x86_64-pc-linux-gnu
Reading makefiles...
Reading makefile `Makefile'...
Updating makefiles....
 Considering target file `Makefile'.
  Looking for an implicit rule for `Makefile'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.o'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.c'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.cc'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.C'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.cpp'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.p'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.f'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.F'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.r'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.s'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.S'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.mod'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.sh'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile,v'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `RCS/Makefile,v'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `RCS/Makefile'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `s.Makefile'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `SCCS/s.Makefile'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.o'.
  Looking for a rule with intermediate file `Makefile.o'.
   Avoiding implicit rule recursion.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.c'.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.cc'.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.C'.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.cpp'.
   Trying pattern rule with stem `Makefile'.
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   Trying implicit prerequisite `RCS/Makefile.o,v'.
   Trying pattern rule with stem `Makefile.o'.
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   Trying implicit prerequisite `s.Makefile.o'.
   Trying pattern rule with stem `Makefile.o'.
   Trying implicit prerequisite `SCCS/s.Makefile.o'.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.c'.
   Looking for a rule with intermediate file `Makefile.c'.
    Avoiding implicit rule recursion.
    Avoiding implicit rule recursion.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.y'.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.l'.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.w'.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.w'.
    Trying pattern rule with stem `Makefile.c'.
    Trying implicit prerequisite `Makefile.c,v'.
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    Trying pattern rule with stem `Makefile.c'.
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    Looking for a rule with intermediate file `Makefile.y'.
     Avoiding implicit rule recursion.
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     Trying pattern rule with stem `Makefile.y'.
     Trying implicit prerequisite `Makefile.y,v'.
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     Trying pattern rule with stem `Makefile.y'.
     Trying implicit prerequisite `RCS/Makefile.y'.
     Trying pattern rule with stem `Makefile.y'.
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     Trying pattern rule with stem `Makefile.y'.
     Trying implicit prerequisite `SCCS/s.Makefile.y'.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.l'.
    Looking for a rule with intermediate file `Makefile.l'.
     Avoiding implicit rule recursion.
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     Trying pattern rule with stem `Makefile.l'.
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     Trying pattern rule with stem `Makefile.l'.
     Trying implicit prerequisite `SCCS/s.Makefile.l'.
    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.w'.
    Looking for a rule with intermediate file `Makefile.w'.
     Avoiding implicit rule recursion.
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     Trying pattern rule with stem `Makefile.w'.
     Trying implicit prerequisite `Makefile.w,v'.
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     Trying pattern rule with stem `Makefile.w'.
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     Trying implicit prerequisite `SCCS/s.Makefile.w'.
    Trying pattern rule with stem `Makefile'.
    Rejecting impossible implicit prerequisite `Makefile.w'.
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   Trying implicit prerequisite `Makefile.cc'.
   Looking for a rule with intermediate file `Makefile.cc'.
    Avoiding implicit rule recursion.
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    Trying implicit prerequisite `Makefile.cc,v'.
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    Trying pattern rule with stem `Makefile.cc'.
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    Trying pattern rule with stem `Makefile.cpp'.
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   Looking for a rule with intermediate file `Makefile.p'.
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    Trying implicit prerequisite `Makefile.web'.
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    Trying pattern rule with stem `Makefile.f'.
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    Trying implicit prerequisite `s.Makefile.f'.
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    Trying implicit prerequisite `SCCS/s.Makefile.f'.
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     Trying implicit prerequisite `RCS/Makefile.r,v'.
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     Trying pattern rule with stem `Makefile.r'.
     Trying implicit prerequisite `SCCS/s.Makefile.r'.
   Trying pattern rule with stem `Makefile'.
   Rejecting impossible implicit prerequisite `Makefile.F'.
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   Looking for a rule with intermediate file `Makefile.s'.
    Avoiding implicit rule recursion.
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    Trying pattern rule with stem `Makefile'.
    Trying implicit prerequisite `Makefile.S'.
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    Trying implicit prerequisite `RCS/Makefile.s,v'.
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    Trying implicit prerequisite `SCCS/s.Makefile.s'.
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    Trying implicit prerequisite `Makefile.S'.
    Looking for a rule with intermediate file `Makefile.S'.
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     Trying pattern rule with stem `Makefile.S'.
     Trying implicit prerequisite `Makefile.S,v'.
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     Trying implicit prerequisite `SCCS/s.Makefile.S'.
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   Rejecting impossible implicit prerequisite `Makefile.S'.
   Trying pattern rule with stem `Makefile'.
   Trying implicit prerequisite `Makefile.mod'.
   Looking for a rule with intermediate file `Makefile.mod'.
    Avoiding implicit rule recursion.
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    Trying pattern rule with stem `Makefile.mod'.
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    Trying implicit prerequisite `s.Makefile.mod'.
    Trying pattern rule with stem `Makefile.mod'.
    Trying implicit prerequisite `SCCS/s.Makefile.mod'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.c'.
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  Rejecting impossible implicit prerequisite `Makefile.C'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.cpp'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.p'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.f'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.F'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.r'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.s'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.S'.
  Trying pattern rule with stem `Makefile'.
  Rejecting impossible implicit prerequisite `Makefile.mod'.
  Trying pattern rule with stem `Makefile'.
  Trying implicit prerequisite `Makefile.sh'.
  Looking for a rule with intermediate file `Makefile.sh'.
   Avoiding implicit rule recursion.
   Trying pattern rule with stem `Makefile.sh'.
   Trying implicit prerequisite `Makefile.sh,v'.
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   Trying implicit prerequisite `RCS/Makefile.sh'.
   Trying pattern rule with stem `Makefile.sh'.
   Trying implicit prerequisite `s.Makefile.sh'.
   Trying pattern rule with stem `Makefile.sh'.
   Trying implicit prerequisite `SCCS/s.Makefile.sh'.
  No implicit rule found for `Makefile'.
  Finished prerequisites of target file `Makefile'.
 No need to remake target `Makefile'.
Updating goal targets....
Considering target file `build'.
 File `build' does not exist.
  Considering target file `makefile.cpp'.
   Looking for an implicit rule for `makefile.cpp'.
   Trying pattern rule with stem `makefile.cpp'.
   Trying implicit prerequisite `makefile.cpp,v'.
   Trying pattern rule with stem `makefile.cpp'.
   Trying implicit prerequisite `RCS/makefile.cpp,v'.
   Trying pattern rule with stem `makefile.cpp'.
   Trying implicit prerequisite `RCS/makefile.cpp'.
   Trying pattern rule with stem `makefile.cpp'.
   Trying implicit prerequisite `s.makefile.cpp'.
   Trying pattern rule with stem `makefile.cpp'.
   Trying implicit prerequisite `SCCS/s.makefile.cpp'.
   No implicit rule found for `makefile.cpp'.
   Finished prerequisites of target file `makefile.cpp'.
  No need to remake target `makefile.cpp'.
 Finished prerequisites of target file `build'.
Must remake target `build'.
g++ -o makefileout makefile.cpp
Putting child 0x01a6de60 (build) PID 6157 on the chain.
Live child 0x01a6de60 (build) PID 6157 
Reaping winning child 0x01a6de60 PID 6157 
Removing child 0x01a6de60 PID 6157 from chain.
Successfully remade target file `build'.

我的问题是：我做错了吗？为什么这么简单的例子会产生如此多的日志？

此外,即使源代码早于最新的make,我的Makefile似乎总是重新编译对象代码.换句话说,我从未见过这样的信息：“没有什么可做的.”

解决方法

我将解决编辑问题：

my Makefile always seems to recompile the object code even if the
source code is older than the latest make

在这个答案.

考虑你的Makefile：

CC = g++
FILES = makefile.cpp
OUT_EXE = makefileout

build: $(FILES)
    $(CC) -o $(OUT_EXE) $(FILES)

这里唯一的目标是构建,这是永远不会构造的东西(这就是为什么你每次都看到编译的原因).对此最简单的解决方法应该是：

CC = g++
FILES = makefile.cpp
OUT_EXE = makefileout

${OUT_EXE}: $(FILES)
    $(CC) -o $(OUT_EXE) $(FILES)

使用新规则make将检查makefileout而不是build,从而提供预期的行为.

如果您想进行更多实验,可以使用Makefile发出以下命令：

rm -f makefileout
touch build
make

你会发现即使可执行文件不存在,make也不会编译它.我告诉你为什么(一个简单的)练习的问题.

（编辑：李大同）

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