在sys / sysmacros.h中定义的主要和次要宏，由< iterator> [英] major and minor macros defined in sys/sysmacros.h pulled in by <iterator>

问题描述

我正在写一个类，它有一个类矩阵结构，我想有一个成员函数，名为minor与矩阵操作相同。这会触发一些错误。在我的系统上的最小测试用例：

I'm writing a class that has a matrix-like structure and I want to have a member function named minor to be the same as the matrix operation. This triggers some errors. A minimal test case on my system:

#include <iterator>
void minor(int row, int col);

编译时，clang提供以下错误：

When compiled, clang provides the following error:

$ clang++ -Weverything -std=c++11 test.cpp 
test.cpp:2:21: error: too many arguments provided to function-like macro invocation
void minor(int row, int col);
                    ^
/usr/include/x86_64-linux-gnu/sys/sysmacros.h:67:10: note: macro 'minor' defined here
# define minor(dev) gnu_dev_minor (dev)
         ^
test.cpp:2:6: error: variable has incomplete type 'void'
void minor(int row, int col);
     ^
2 errors generated.
$

sys / sysmacros.h的相关部分是：

The relevant portion of sys/sysmacros.h is:

/* Access the functions with their traditional names.  */
# define major(dev) gnu_dev_major (dev)
# define minor(dev) gnu_dev_minor (dev)
# define makedev(maj, min) gnu_dev_makedev (maj, min)

显然，这些特定的宏可能是＃undef'd，但似乎很愚蠢的例句和minor将被定义为宏，特别是在拉取部分C ++标准库时。是否有某些原因需要定义？这是我使用的标准库中的错误吗？ （libstdc ++ 4.8.2在Debian测试中）

Clearly, these specific macros could be #undef'd, but it seems quite silly that such routine words as major and minor would be defined as macros, particularly when pulling in part of the C++ standard library. Is there some reason these need to be defined? Is this a bug in the standard library I'm using? (libstdc++ 4.8.2 as in Debian testing)

推荐答案

根据C ++标准，这些名称不应保留到实现

According to the C++ standard those names shouldn't be reserved to the implementation and thus be available.

根据 man 3 makedev ：

makedev（），major（）和minor（）函数没有在
POSIX.1中指定，但是存在于许多其他系统上

The makedev(), major(), and minor() functions are not specified in POSIX.1, but are present on many other systems

和

这些接口定义为宏。从glibc 2.3.3开始，它们
是三个GNU特定函数的别名：
gnu_dev_makedev（），gnu_dev_major（）和gnu_dev_minor（）。后面的
名称是导出的，但是传统名称更容易移植。

These interfaces are defined as macros. Since glibc 2.3.3, they have been aliases for three GNU-specific functions: gnu_dev_makedev(), gnu_dev_major(), and gnu_dev_minor(). The latter names are exported, but the traditional names are more portable.

看起来，向后兼容性（例如 https://bugzilla.redhat.com/show_bug.cgi?id=130601 ） 。

It seems that they aren't removed for backward compatibility (e.g. https://bugzilla.redhat.com/show_bug.cgi?id=130601).

我想你可以#undef没有重大问题（许多项目以这种方式进行）。

I think you could #undef them without major issues (many projects proceed in this way).

使用 G ++ / CLANG / MSVC 您也可以做类似的操作：

With G++/CLANG/MSVC you could also do something like:

#pragma push_macro("minor")
#undef minor

// do what you need

#pragma pop_macro("minor")

这很丑陋，但有助于命名冲突。

It's ugly, but helps with naming conflicts.

此外，根据代码的结构，这个技巧可能是有用的：

Moreover, depending on how your code is structured, this trick can be useful:

#define minor(dev) gnu_dev_major(dev)

void (minor)(int row, int col) { /* ... */ }

在函数定义行中，'minor'后的字符是一个右括号，因此它不是一个宏调用。

In the function definition line, the character after 'minor' is a close parenthesis, so it is not a macro invocation.

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