在C++ Builder中创建含Eigen库的DLL编译报错求助

环境与问题 #

使用C++ Builder 11 CE、Eigen 3.4.0，尝试将集成Eigen库的程序打包为动态链接库（.dll）时，在DLL的cpp文件中引入#include <Eigen/Eigen>后编译，出现大量未声明标识符错误（如fabsf、expf、logf等）。

错误信息 #

[bcc32c Error] MathFunctions.h(1304): use of undeclared identifier 'fabsf'
[bcc32c Error] MathFunctions.h(1310): use of undeclared identifier 'fabs'
[bcc32c Error] MathFunctions.h(1318): use of undeclared identifier 'fabsl'
[bcc32c Error] Half.h(660): no member named 'expf' in the global namespace
[bcc32c Error] Half.h(671): no member named 'logf' in the global namespace
[bcc32c Error] Half.h(678): no member named 'log10f' in the global namespace
[bcc32c Error] Half.h(681): no member named 'logf' in the global namespace
[bcc32c Error] Half.h(689): no member named 'sqrtf' in the global namespace
[bcc32c Error] Half.h(693): no member named 'powf' in the global namespace
[bcc32c Error] Half.h(696): no member named 'sinf' in the global namespace
[bcc32c Error] Half.h(699): no member named 'cosf' in the global namespace
[bcc32c Error] Half.h(702): no member named 'tanf' in the global namespace
[bcc32c Error] Half.h(705): no member named 'tanhf' in the global namespace
[bcc32c Error] Half.h(708): no member named 'asinf' in the global namespace
[bcc32c Error] Half.h(711): no member named 'acosf' in the global namespace
[bcc32c Error] Half.h(718): no member named 'floorf' in the global namespace
[bcc32c Error] Half.h(726): no member named 'ceilf' in the global namespace
[bcc32c Error] Half.h(730): no member named 'rintf' in the global namespace
[bcc32c Error] Half.h(733): no member named 'roundf' in the global namespace
[bcc32c Error] Half.h(736): no member named 'fmodf' in the global namespace
[bcc32c Error] BFloat16.h(494): no member named 'expf' in the global namespace
[bcc32c Error] BFloat16.h(500): no member named 'logf' in the global namespace
[bcc32c Error] BFloat16.h(506): no member named 'log10f' in the global namespace
[bcc32c Error] BFloat16.h(509): no member named 'logf' in the global namespace
[bcc32c Error] BFloat16.h(512): no member named 'sqrtf' in the global namespace
[bcc32c Error] BFloat16.h(515): no member named 'powf' in the global namespace
[bcc32c Error] BFloat16.h(518): no member named 'sinf' in the global namespace
[bcc32c Error] BFloat16.h(521): no member named 'cosf' in the global namespace
[bcc32c Error] BFloat16.h(524): no member named 'tanf' in the global namespace
[bcc32c Error] BFloat16.h(527): no member named 'asinf' in the global namespace
[bcc32c Error] BFloat16.h(530): no member named 'acosf' in the global namespace
[bcc32c Error] BFloat16.h(533): no member named 'atanf' in the global namespace
[bcc32c Error] BFloat16.h(536): no member named 'sinhf' in the global namespace
[bcc32c Error] BFloat16.h(539): no member named 'coshf' in the global namespace
[bcc32c Error] BFloat16.h(542): no member named 'tanhf' in the global namespace
[bcc32c Error] BFloat16.h(546): no member named 'asinhf' in the global namespace
[bcc32c Error] BFloat16.h(549): no member named 'acoshf' in the global namespace
[bcc32c Error] BFloat16.h(552): no member named 'atanhf' in the global namespace
[bcc32c Error] BFloat16.h(556): no member named 'floorf' in the global namespace
[bcc32c Error] BFloat16.h(559): no member named 'ceilf' in the global namespace
[bcc32c Error] BFloat16.h(562): no member named 'rintf' in the global namespace
[bcc32c Error] BFloat16.h(565): no member named 'roundf' in the global namespace
[bcc32c Error] BFloat16.h(568): no member named 'fmodf' in the global namespace
[bcc32c Error] BFloat16.h(585): no member named 'fminf' in the global namespace
[bcc32c Error] BFloat16.h(590): no member named 'fmaxf' in the global namespace
Failed

现有DLL代码 #

#include <Eigen/Eigen>

#pragma hdrstop
#pragma argsused


extern "C" double __declspec(dllexport) __stdcall Sum(double a, double b) {
    return a +b;
}

extern "C" int _libmain(unsigned long reason)
{
    return 1;
}

解决办法 #

1. 提前引入标准数学头文件 #

Eigen依赖C标准库的数学函数，需在引入Eigen前包含<cmath>，确保编译器能识别这些函数。修改后的代码如下：

#include <cmath>
#include <Eigen/Eigen>

#pragma hdrstop
#pragma argsused

extern "C" double __declspec(dllexport) __stdcall Sum(double a, double b) {
    return a +b;
}

extern "C" int _libmain(unsigned long reason)
{
    return 1;
}

2. 添加编译器预定义宏 #

bcc32c编译器需要显式定义宏来启用C99标准的数学函数，操作步骤：

• 打开项目选项（Project -> Options）
• 切换到C++ Compiler -> Preprocessor
• 在Defined macros中添加_USE_C99_MATH和__STDC_WANT_IEC_60559_BFP_EXT__

3. 强制Eigen使用标准库数学函数 #

如果前两步无效，可在引入Eigen前添加Eigen专属配置宏，强制其依赖标准库函数：

#define EIGEN_USE_STD_MATH_FUNCTIONS
#include <cmath>
#include <Eigen/Eigen>

4. 确认编译标准版本 #

确保项目使用C++11及以上标准：

• 打开项目选项 -> C++ Compiler -> Language
• 将C++ Language Version设置为C++17或C++11

内容的提问来源于stack exchange，提问作者Scarlet