MXNet C++包引入dmlc/base.h时编译报错求助

问题背景 #

已完成MXNet C++包的编译安装流程：

cd mxnet
mkdir build
cd build
cmake -DUSE_CPP_PACKAGE=1 ..
cmake --build . --target install

但在代码中引入头文件#include "mxnet-cpp/MxNetCpp.h"后，出现3个与dmlc库相关的编译错误。

具体错误信息 #

1. /usr/local/include/dmlc/base.h:247:1: error: template with C linkage
2. /usr/local/include/dmlc/base.h:260:1: error: template with C linkage
3. /usr/local/include/dmlc/base.h:282:20: error: conflicting declaration of C function ‘const char* dmlc::BeginPtr(const string&)’

完整编译日志：

In file included from /usr/local/include/dmlc/endian.h:9,
                 from /usr/include/x86_64-linux-gnu/sys/types.h:176,
                 from /usr/include/stdlib.h:395,
                 from /usr/include/c++/11/cstdlib:75,
                 from /usr/include/c++/11/ext/string_conversions.h:41,
                 from /usr/include/c++/11/bits/basic_string.h:6608,
                 from /usr/include/c++/11/string:55,
                 from /usr/local/include/mxnet-cpp/executor.hpp:31,
                 from /usr/local/include/mxnet-cpp/MxNetCpp.h:29,
                 from /home/stathis/Documents/Documents/Documents/Untitled.cpp:1:
/usr/local/include/dmlc/base.h:247:1: error: template with C linkage
  247 | template<typename T>
      | ^~~~~~~~
In file included from /usr/include/features.h:486,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/c++config.h:586,
                 from /usr/include/c++/11/bits/stl_algobase.h:59,
                 from /usr/include/c++/11/vector:60,
                 from /usr/local/include/mxnet-cpp/executor.hpp:29,
                 from /usr/local/include/mxnet-cpp/MxNetCpp.h:29,
                 from /home/stathis/Documents/Documents/Documents/Untitled.cpp:1:
/usr/include/x86_64-linux-gnu/sys/types.h:27:1: note: 'extern "C"' linkage started here
   27 | __BEGIN_DECLS
      | ^~~~~~~~~~~~~
In file included from /usr/local/include/dmlc/endian.h:9,
                 from /usr/include/x86_64-linux-gnu/sys/types.h:176,
                 from /usr/include/stdlib.h:395,
                 from /usr/include/c++/11/cstdlib:75,
                 from /usr/include/c++/11/ext/string_conversions.h:41,
                 from /usr/include/c++/11/bits/basic_string.h:6608,
                 from /usr/include/c++/11/string:55,
                 from /usr/local/include/mxnet-cpp/executor.hpp:31,
                 from /usr/local/include/mxnet-cpp/MxNetCpp.h:29,
                 from /home/stathis/Documents/Documents/Documents/Untitled.cpp:1:
/usr/local/include/dmlc/base.h:260:1: error: template with C linkage
  260 | template<typename T>
      | ^~~~~~~~
In file included from /usr/include/features.h:486,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/11/bits/c++config.h:586,
                 from /usr/include/c++/11/bits/stl_algobase.h:59,
                 from /usr/include/c++/11/vector:60,
                 from /usr/local/include/mxnet-cpp/executor.hpp:29,
                 from /usr/local/include/mxnet-cpp/MxNetCpp.h:29,
                 from /home/stathis/Documents/Documents/Documents/Untitled.cpp:1:
/usr/include/x86_64-linux-gnu/sys/types.h:27:1: note: 'extern "C"' linkage started here
   27 | __BEGIN_DECLS
      | ^~~~~~~~~~~~~
In file included from /usr/local/include/dmlc/endian.h:9,
                 from /usr/include/x86_64-linux-gnu/sys/types.h:176,
                 from /usr/include/stdlib.h:395,
                 from /usr/include/c++/11/cstdlib:75,
                 from /usr/include/c++/11/ext/string_conversions.h:41,
                 from /usr/include/c++/11/bits/basic_string.h:6608,
                 from /usr/include/c++/11/string:55,
                 from /usr/local/include/mxnet-cpp/executor.hpp:31,
                 from /usr/local/include/mxnet-cpp/MxNetCpp.h:29,
                 from /home/stathis/Documents/Documents/Documents/Untitled.cpp:1:
/usr/local/include/dmlc/base.h:282:20: error: conflicting declaration of C function 'const char* dmlc::BeginPtr(const string&)'
  282 | inline const char* BeginPtr(const std::string &str) {
      |                    ^~~~~~~~
/usr/local/include/dmlc/base.h:273:14: note: previous declaration 'char* dmlc::BeginPtr(std::string&)'
  273 | inline char* BeginPtr(std::string &str) {  // NOLINT(*)
      |              ^~~~~~~~
make[1]: *** [Documents.mk:97: ../build-Debug/Documents/Untitled.cpp.o] Error 1
make[1]: Leaving directory '/home/stathis/Documents/Documents/Documents'
make: *** [Makefile:5: All] Error 2
==== build ended with errors (3 errors, 3 warnings) ===

解决建议 #

1. 修复模板C链接冲突问题 #

错误根源是系统C头文件sys/types.h在extern "C"块内引入了dmlc/endian.h，导致C++模板被当作C代码处理。可以用以下两种方法解决：

• 调整头文件包含顺序：在你的C++代码最开头先包含mxnet-cpp/MxNetCpp.h，再包含其他系统头文件，避免系统C头文件先触发dmlc头文件的加载。
• 修改dmlc头文件：编辑/usr/local/include/dmlc/endian.h，给base.h的包含语句加上C++环境判断：

  #ifdef __cplusplus
  #include "base.h"
  #else
  // 保留原有的C兼容代码
  #endif
  

2. 修复BeginPtr声明冲突问题 #

这是base.h内的函数重载被编译器误判为C函数冲突导致的，可通过以下方式解决：

• 统一函数返回值：将base.h中两个BeginPtr函数的返回值统一，比如把非const版本改为inline const char* BeginPtr(std::string &str)。
• 明确C++链接声明：给两个BeginPtr函数加上extern "C++"包裹，告诉编译器这是C++函数：

  #ifdef __cplusplus
  extern "C++" {
  #endif
  inline char* BeginPtr(std::string &str) { /* 原函数实现 */ }
  inline const char* BeginPtr(const std::string &str) { /* 原函数实现 */ }
  #ifdef __cplusplus
  }
  #endif
  

3. 其他可行方案 #

• 重新编译MXNet并指定内置dmlc：在cmake时添加参数，强制使用MXNet自带的dmlc库，避免系统中旧版本dmlc冲突：

  cmake -DUSE_CPP_PACKAGE=1 -DBUILD_DMLC_FROM_SOURCE=1 ..
  

• 清理系统中多余的dmlc版本：检查系统中是否存在多个路径的dmlc头文件，删除旧版本，确保只有MXNet安装的/usr/local/include/dmlc/目录有效。

内容的提问来源于stack exchange，提问作者Stathis G.