鉴于存在危险，为什么项目要使用-I include开关？ [英] Why do projects use the -I include switch given the dangers?

问题描述

阅读了GCC中 -I 开关的详细信息后，我很震惊地发现在命令行上使用它会覆盖系统包含的内容。从预处理器文档

Reading the fine print of the -I switch in GCC, I'm rather shocked to find that using it on the command line overrides system includes. From the preprocessor docs

您可以使用 -I 覆盖系统头文件，替换您自己的版本，因为已搜索这些目录在标准系统头文件目录之前。

"You can use -I to override a system header file, substituting your own version, since these directories are searched before the standard system header file directories."

它们似乎不是在撒谎。在带有GCC 7的两个不同的Ubuntu系统上，如果我创建文件 endian.h ：

They don't seem to be lying. On two different Ubuntu systems with GCC 7, if I create a file endian.h:

#error "This endian.h shouldn't be included"

...然后在同一目录中创建 main.cpp （或main.c，相同的区别）：

...and then in the same directory create a main.cpp (or main.c, same difference):

#include <stdlib.h>
int main() {}

然后使用 g ++ main进行编译.cpp -I。 -o main （或叮当声，相同的区别）给我：

Then compiling with g++ main.cpp -I. -o main (or clang, same difference) gives me:

In file included from /usr/include/x86_64-linux-gnu/sys/types.h:194:0,
                 from /usr/include/stdlib.h:394,
                 from /usr/include/c++/7/cstdlib:75,
                 from /usr/include/c++/7/stdlib.h:36,
                 from main.cpp:1:
./endian.h:1:2: error: #error "This endian.h shouldn't be included"

因此stdlib.h包括此类型。 h文件，该文件在第194行仅显示 #include< endian.h> 。我明显的误解（也许还有其他人的误解）是尖括号会阻止这种情况，但是-我比我想象的要强。

So stdlib.h includes this types.h file, which on line 194 just says #include <endian.h>. My apparent misconception (and perhaps that of others) was that the angle brackets would have prevented this, but -I is stronger than I'd thought.

尽管不牢固足够，因为您甚至无法通过首先在命令行上粘贴/ usr / include来解决它，因为：

Though not strong enough, because you can't even fix it by sticking /usr/include in on the command line first, because:

如果标准系统包含目录，或者使用 -isystem 指定的目录，也使用 -I ， -I 选项将被忽略。该目录仍在搜索，但作为系统目录在系统包含链中的正常位置。

"If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain."

实际上是 g ++ -v main.cpp -I / usr / include -I的详细输出。 -o main 将/ usr / include留在列表的底部：

Indeed, the verbose output for g++ -v main.cpp -I/usr/include -I. -o main leaves /usr/include at the bottom of the list:

#include "..." search starts here:
#include <...> search starts here:
 .
 /usr/include/c++/7
 /usr/include/x86_64-linux-gnu/c++/7
 /usr/include/c++/7/backward
 /usr/lib/gcc/x86_64-linux-gnu/7/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include

让我惊讶。我想让这个问题成为问题：

Color me surprised. I guess to make this a question:

大多数项目使用 -I 考虑到这个极其严重的问题？您可以基于偶然的名称冲突在系统上覆盖任意标头。不是每个人都应该使用 -iquote 代替吗？

What legitimate reason is there for most projects to use -I considering this extremely serious issue? You can override arbitrary headers on systems based on incidental name collisions. Shouldn't pretty much everyone be using -iquote instead?

推荐答案

-I 超过 -iquote 有什么正当理由？ -I 是标准化的（至少由 POSIX ），而 -iquote 不是。 （实际上，我使用的是 -I ，因为tinycc（我希望我的项目与之编译的编译器之一）不支持 -iquote 。）

What legitimate reasons are there for -I over -iquote? -I is standardized (at least by POSIX) while -iquote isn't. (Practically, I'm using -I because tinycc (one of the compilers I want my project to compile with) doesn't support -iquote.)

在存在危险的情况下，如何使用 -I 管理项目？您将把include包裹在一个目录中，并使用-I添加包含该目录的目录。

How do projects manage with -I given the dangers? You'd have the includes wrapped in a directory and use -I to add the directory containing that directory.

• 文件系统： includes / mylib / endian.h


• 命令行： -Iincludes


• C / C ++文件： #include mylib / endian.h //或< mylib / endian.h>

• filesystem: includes/mylib/endian.h
• command line: -Iincludes
• C/C++ file: #include "mylib/endian.h" //or <mylib/endian.h>

有了这个，只要您不冲突 mylib 名称，您就不会冲突（至少就标题名称而言）。

With that, as long as you don't clash on the mylib name, you don't clash (at least as far header names are concerned).

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