编译器无法找到与QUOT; aligned_alloc＆QUOT;功能 [英] compiler can't find "aligned_alloc" function

问题描述

试图让一个便携式的函数，在堆上分配对齐功能。

找到aligned_alloc，我认为这是stdlib.h中，但海湾合作委员会似乎不这么认为。

  

错误：aligned_alloc在此范围未声明

使用gcc旗子

-std = C ++ 11 -m64

试图导入

 的#include＆LT;＆stdlib.h中GT;
＃包括LT＆; cstdlib＆GT;
 

解决方案

aligned_alloc 在C11定义。据（还）没有定义用于C ++，尽管它可能在C ++中17中显示。 （也就是说，它是不是在列表中（目前）209的功能在标准C库，预计将在标准C ++库可参见C ++标准的附录C）。

如果你想用gcc使用它（或者更确切地说，与G ++），你应该使用功能测试宏 _ISOC11_SOURCE 。像所有的功能测试宏，宏必须在每一个需要它之前的任何文件的#define 'D 的#include 。 [见注1]（功能测试宏不会，如果你用 -std = C11 编译一个C程序是必要的。）

我发现从男人aligned_alloc 正确的功能测试宏：

  

特性测试的glibc的宏要求（见feature_test_macros（7））：

  posix_memalign（）：_POSIX_C_SOURCE＆GT; = 200112L || _XOPEN_SOURCE＆GT; = 600  aligned_alloc（）：_ISOC11_SOURCE
 

作为指示，你可以阅读

 人7 feature_test_macros
 

有关功能测试宏的详细信息，包括glibc的认可宏的列表，并在每一个应用。

的 aligned_alloc 手册页也记录了非常相似的 posix_memalign 功能，这一直以来发行了POSIX标准的一部分6，并且具有不同的（更常见的）功能测试宏，如上所述。 posix_memalign 应该可以移植到任何Posix的系统，这可能会或可能不会包括比那些接受C ++使用C11功能的多个系统。

注释

1. 这意味着你不应该把的#define 在头文件，因为头文件不能被包含之前，首先包括:)但是，如果你使用的东西像的#includeconfig.h中来包括平台的定义，每一个源文件与开始的#includeconfig.h中，任何其他之前的#include 和的#define 发生在配置。 ^ h 之前的任何的#include ，你应该确定。

Trying to get a portable function to allocate on heap with aligned feature.

Found "aligned_alloc", which I think is in stdlib.h but gcc seems to not think so

error: 'aligned_alloc' was not declared in this scope

using gcc with flags -std=c++11 -m64

tried importing

#include <stdlib.h>
#include <cstdlib>

解决方案

aligned_alloc is defined in C11. It is not (yet) defined for C++, although it may show up in C++17. (That is, it is not in the list of (currently) 209 functions in the standard C library which are expected to be available in the standard C++ library. See Appendix C of the C++ standard.)

If you want to use it with gcc (or, more specifically, with g++), you should use the feature test macro _ISOC11_SOURCE. Like all feature test macros, this macro must be #define'd in every file which requires it before any #include. [See note 1] (The feature test macro would not be necessary if you were compiling a C program with -std=c11.)

I found the correct feature test macro from man aligned_alloc:

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

  posix_memalign(): _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

  aligned_alloc(): _ISOC11_SOURCE

As that indicates, you can read

man 7 feature_test_macros

for more information on feature test macros, including a list of the macros recognized by glibc, and when each one applies.

The aligned_alloc manpage also documents the very similar posix_memalign function, which has been part of the Posix standard since Issue 6, and which has different (and more common) feature test macros, as indicated above. posix_memalign should be portable to any Posix system, which might or might not include more systems than those that accept the use of a C11 function in C++.

Notes

1. This means you shouldn't put the #define in a header file, since the header file cannot be included before the first include :) However, if you use something like #include "config.h" to include platform definitions, and every source file starts with #include "config.h", prior to any other #include, and the #define occurs in config.h prior to any #include, you should be OK.

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