编译器错误 C2719 & Eigen库出现的对齐问题

注意收集错误信息，通过“输出”窗口，定位到具体代码行！！！

解决方案：

http://eigen.tuxfamily.org/dox/TopicStlContainers.html

eigen 3.1.2有 bug,   

更新daily build版本： (官网 https://bitbucket.org/eigen/eigen/)

hg clone https://bitbucket.org/eigen/eigen/

并修改   RealScalar p => const RealScalar& p

关于为何更改的网页找不到了。。。 大致意思是这个： http://eigen.tuxfamily.org/bz/show_bug.cgi?id=83

msvc2008才会出现此错误，2010没有。

解释大致为：

error C2719: '_Val': formal parameter with __declspec(align('16')) won't be aligned?

It is a known issue that stl::vector cannot properly contain aligned data, such as D3DXMATRIXA16. One poster pinned the root cause (or at least, one of them?): the declaration of vector::resize passes the aligned data by value, and not as const reference. Several workarounds were suggested in that thread, the safest being dropping stl::vector altogether. You might also want to fix the stl headers yourself and recompile - this actually may be easier than it sounds, but I haven't done so myself.

EDIT: links are now broken (thanks @David Menard), here's an alternative, more elaborate answer.

The issue is fixed in VS2012RC - here's a link to a corresponding connect issue. Turns out it was actually an issue in the C++ standard itself, fixed in 2008.

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(zz)使用Eigen库出现的对齐问题。

2012-03-13 19:34:36| 分类：reproduct| 标签：eigenvs2010|字号大中小订阅

error C2719: '_Val': formal parameter with __declspec(align('16')) won't be aligned
2012-02-09 12:42

英文提示:error C2719: 'p': formal parameter with __declspec(align('16')) won't be aligned 中文提示:error C2719: “p”: 具有 __declspec(align('16')) 的形参将不被对齐 导致整个现象的主要原因是使用了Eigen库，Eigen为了使用SSE加速，所以内存分配上使用了128位的指针。 更加准确的说法： “First, "fixed-size" should be clear: an Eigen object has fixed size if its number of rows and its number of columns are fixed at compile-time. So for example Matrix3f has fixed size, but MatrixXf doesn't (the opposite of fixed-size is dynamic-size). The array of coefficients of a fixed-size Eigen object is a plain "static array", it is not dynamically allocated. For example, the data behind a Matrix4f is just a "float array[16]". Fixed-size objects are typically very small, which means that we want to handle them with zero runtime overhead -- both in terms of memory usage and of speed. Now, vectorization (both SSE and AltiVec) works with 128-bit packets. Moreover, for performance reasons, these packets need to be have 128-bit alignment. So it turns out that the only way that fixed-size Eigen objects can be vectorized, is if their size is a multiple of 128 bits, or 16 bytes.Eigen will then request 16-byte alignment for these objects, and henceforth rely on these objects being aligned so no runtime check for alignment is performed.” 解决方案： 分为四种情况： Cause 1: Structures having Eigen objects as members Cause 2: STL Containers Cause 3: Passing Eigen objects by value Cause 4: Compiler making a wrong assumption on stack alignment (for instance GCC on Windows) 每种情况可以对照官方的说法。可以参考如下链接 http://eigen.tuxfamily.org/dox/TopicUnalignedArrayAssert.html 在此不再重复表述。

http://eigen.tuxfamily.org/dox/TopicUnalignedArrayAssert.html#c3

Table of contents

• Where in my own code is the cause of the problem?
• Cause 1: Structures having Eigen objects as members
• Cause 2: STL Containers
• Cause 3: Passing Eigen objects by value
• Cause 4: Compiler making a wrong assumption on stack alignment (for instance GCC on Windows)
• Explanation
• I don't care about vectorization, how do I get rid of that stuff?

编译器错误 C2719

Visual Studio 2008

其他版本

• Visual Studio 2012
• Visual Studio 2010
• Visual Studio 2005

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更新：2007 年 11 月

错误消息

“parameter”: 具有 __declspec(align('#')) 的形参将不被对齐

函数参数中不允许使用 align__declspec 修饰符。

下面的示例生成 C2719：

复制

// C2719.cpp
void func(int __declspec(align(32)) i);   // C2719
// try the following line instead
// void func(int i);