Question

我一直在尝试编写一些错误保护条款，用于识别第三方提供给我们的dll中的问题。这个DLL可能存在问题（内存异常，浮点错误等），并且能够在不访问源代码的情况下识别这些错误是有利的。

我从各种SEH错误处理例程中收集了一些东西，但是虽然它有效，但它有几个......不一致。我试图孤立每一个，我将逐个问一个问题。

这与使用_controlfp_s设置和重置浮点错误行为有关。

// For floating point protection ---------
#include <float.h>      // defines of _EM_OVERFLOW, etc.
#include <string.h>     // strncpy_s & strncat_s
#include <stdlib.h>     // malloc
#include <excpt.h>      // EXCEPTION_EXECUTE_HANDLER
#include <iostream>     // cout
#include <bitset>       // bitset
#include <conio.h>      // _kbhit
#pragma fenv_access (on)
// ---------------------------------------


const unsigned int SERIOUS_FP_EXCEPTIONS = _EM_DENORMAL | _EM_ZERODIVIDE | _EM_INVALID;
const unsigned int MINOR_FP_EXCEPTIONS = _EM_OVERFLOW | _EM_UNDERFLOW | _EM_INEXACT;

int main(int argc, char[])
{
    double numerator = 1.0;
    double denominator = 0.0;
    double result = 0.0;


    unsigned int _previous_floating_point_control;
    unsigned int _current_floating_point_control;

    _controlfp_s(&_current_floating_point_control, 0, 0);
    std::cout << "Floating point word originally:       " << std::bitset<32>(_current_floating_point_control) << std::endl;
    std::cout << "New settings to add:                  " << std::bitset<32>(MINOR_FP_EXCEPTIONS) << std::endl;
    std::cout << "With the mask:                        " << std::bitset<32>(_MCW_EM) << std::endl;

    _controlfp_s(&_previous_floating_point_control, MINOR_FP_EXCEPTIONS, _MCW_EM);      // This should appear to work, according to the documentation.
    std::cout << "Floating point word cached:           " << std::bitset<32>(_previous_floating_point_control) << std::endl;

    /* This works:
    _controlfp_s(&_previous_floating_point_control, 0, 0);      // This should appear to work, according to the documentation.
    _controlfp_s(nullptr, MINOR_FP_EXCEPTIONS, _MCW_EM);      // This should appear to work, according to the documentation.
    std::cout << "Floating point word cached:           " << std::bitset<32>(_previous_floating_point_control) << std::endl;
    */

    _controlfp_s(&_current_floating_point_control, 0, 0);
    std::cout << "Floating point word used:             " << std::bitset<32>(_current_floating_point_control) << std::endl;

    __try {
        result = numerator / denominator;
        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);
        std::cout << "No error detected." << std::endl;
    }
    __except (EXCEPTION_EXECUTE_HANDLER)
    {
        std::cout << "Error code is:                        " << std::bitset<32>(GetExceptionCode()) << std::endl;
        if ((GetExceptionCode() & _EM_INVALID) || (GetExceptionCode() & _EM_ZERODIVIDE) || (GetExceptionCode() & _EM_DENORMAL))
            std::cout << "ERROR! Serious floating point error!" << std::endl;
        else
            std::cout << "Something else..." << std::endl;

        _controlfp_s(NULL, _previous_floating_point_control, _MCW_EM);

        _controlfp_s(&_current_floating_point_control, 0, 0);
        std::cout << "Floating point word reset to:         " << std::bitset<32>(_current_floating_point_control) << std::endl;

    }

    std::cout << "result = " << result << std::endl;

    while (!_kbhit())   // Wait until a key is pressed to close console.
    { }
}

这会产生：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000000111
Floating point word used:             00000000000010010000000000000111
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000000111
result = 0

请注意，_previous_floating_point_control实际上已设置为 new 值，因此在最后重置它的努力不会做任何事情。

这是正确的行为（分两步使用_controlfp_s）：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000000111
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000011111
result = 0

我认为这是一个错误，因为我有办法绕过它，我很乐意忽略它。

但情况会变得更糟：如果你注意到，上面的例子（有效）将浮点字设置为MINOR_FP_EXCEPTIONS，这成功地获取了SERIOUS_FP_EXCEPTIONS。如果我尝试替换它：

_controlfp_s(&_previous_floating_point_control, SERIOUS_FP_EXCEPTIONS, _MCW_EM);

收率：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000010000000000000011000
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000011000
No error detected.
result = 1.#INF


_controlfp_s(&_previous_floating_point_control, 0, _MCW_EM);

收率：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000000000000000000000000
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000000000
Error code is:                        11000000000000000000001010110101
ERROR! Serious floating point error!
Floating point word reset to:         00000000000010010000000000011111
result = 0

和： _controlfp_s（nullptr，_MCW_EM，_MCW_EM）; 产率：

Floating point word originally:       00000000000010010000000000011111
New settings to add:                  00000000000010000000000000011111
With the mask:                        00000000000010000000000000011111
Floating point word cached:           00000000000010010000000000011111
Floating point word used:             00000000000010010000000000011111
No error detected.
result = 1.#INF

总结一下：

_controlfp_s不会“获取”旧的浮点词作为“set”的副产品，但是如果你在单独的操作中执行它。
要捕获严重的浮点错误，您需要设置_controlfp_s以查找次要的f.p.e.s而不是主要的。
[未能识别除零的问题是其他问题之一]

我只是误解了整个地区吗？

Answer 1

我想我会对这个答案嗤之以鼻，因为我对我的相关问题有一个非常有用的回答：How do I interpret GetExceptionCode results when using SEH?。

通过实验，似乎_controlfp_s的新设置是要忽略的异常，而不是响应的异常。我找到了关于此的官方文件......不清楚。

关于将旧值返回到f.p.的问题在设置一个新词时说：我认为这是一个错误 - 或者至少是不受欢迎的行为。文档明确说明_controlfp_s将在掩码为0时填充旧值，但不提及其他情况。在几乎所有类似的函数中，我希望你能够在一个操作中执行get和set - 而不是一个作为get 或集合运行的函数。

使用SEH时如何使用_controlfp_s？

1 个答案: