不能使用包含 math.h 和 g++ 7 (Raspberry PI） 的 C 库

Cannot use C libraries that include math.h with g++ 7 (Raspberry PI)

本文关键字：PI Raspberry g++ 包含 math 不能      更新时间：2023-10-16

我已经为Raspberry PI构建了GCC 7.2.0，并使用前缀/usr/local/gcc-7.2.0安装了它(使用本教程(。每当我尝试编译一个包含 C 库的源代码时，而 C 库又包含math.h我都会收到奇怪的错误。下面是一个最小示例：

extern "C" {
#include <libavcodec/avcodec.h>
}
int main() {
    return 0;
}

注意：这里需要extern "C"，因为avcodec.h没有。我确定这不是问题所在，因为我尝试删除它但仍然收到相同的错误。

使用/usr/local/gcc-7.2.0/bin/g++-7.2.0 main.cpp编译，出现以下错误：

In file included from /usr/local/include/libavutil/common.h:36:0,
                 from /usr/local/include/libavutil/avutil.h:296,
                 from /usr/local/include/libavutil/samplefmt.h:24,
                 from /usr/local/include/libavcodec/avcodec.h:31,
                 from main.cpp:4:
/usr/local/gcc-7.2.0/include/c++/7.2.0/math.h:65:12: error: ‘constexpr bool std::isinf(double)’ conflicts with a previous declaration
 using std::isinf;
            ^~~~~
In file included from /usr/include/features.h:374:0,
                 from /usr/include/errno.h:28,
                 from /usr/local/include/libavcodec/avcodec.h:30,
                 from main.cpp:4:
/usr/include/arm-linux-gnueabihf/bits/mathcalls.h:201:1: note: previous declaration ‘int isinf(double)’
 __MATHDECL_1 (int,isinf,, (_Mdouble_ __value)) __attribute__ ((__const__));
 ^
In file included from /usr/local/include/libavutil/common.h:36:0,
                 from /usr/local/include/libavutil/avutil.h:296,
                 from /usr/local/include/libavutil/samplefmt.h:24,
                 from /usr/local/include/libavcodec/avcodec.h:31,
                 from main.cpp:4:
/usr/local/gcc-7.2.0/include/c++/7.2.0/math.h:66:12: error: ‘constexpr bool std::isnan(double)’ conflicts with a previous declaration
 using std::isnan;
            ^~~~~
In file included from /usr/include/features.h:374:0,
                 from /usr/include/errno.h:28,
                 from /usr/local/include/libavcodec/avcodec.h:30,
                 from main.cpp:4:
/usr/include/arm-linux-gnueabihf/bits/mathcalls.h:234:1: note: previous declaration ‘int isnan(double)’
 __MATHDECL_1 (int,isnan,, (_Mdouble_ __value)) __attribute__ ((__const__));
 ^

您有全局命名空间冲突，因为 math.h 在全局命名空间中声明 C 名称。

问题出在您的 mathcalls.h 版本中 有一个修补程序可以通过在使用 C++11 或更高版本时有条件地不定义isnan和isinf来修复它。这是mathcalls.h的补丁。

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