c++ - union 结构数组的初始化太多

Question

这段代码只是为了测试我对结构数组访问的了解。当我执行这段代码时，它给了我两个 many initializes for param 的错误。请帮助我了解错误并解决此问题。我试图重用已经被某人解决的代码。我关于用参数 Param_u param 填充结构的问题

#include <iostream>
#include <stdio.h>
#include <string.h>


#define ARRAY_COUNT(arr) (sizeof (arr) / sizeof *(arr))

typedef union {
    struct {    // Function parameters
        int *array;
        size_t size;
    };
    struct {    // Function return value
        float mean;
        int Median;
    };
} Param_u;

int main() {
    int array_1[] = {1, 2, 3, 4, 5};
    int  ret1, ret2;

    // Fill the Struct with parameters
    Param_u param = {
        .array = array_1,
        .size = ARRAY_COUNT(array_1),
    };
    return 0;
}

Answer 1

这不是标准的 C++。您正在使用匿名 struct 和指定的初始值设定项(C99 功能)。 C++ 不支持那个。在 clang++ 和 g++ 上启用 -pedantic-errors 选项。参见 this问题了解更多详情。您正在使用特定于编译器的扩展，因此您的程序不可移植。

查看现场演示 here .

clang++ 提供以下诊断:

Error(s):

source_file.cpp:12:5: error: anonymous structs are a GNU extension [-Werror,-Wgnu-anonymous-struct]
    struct {    // Function parameters
    ^
source_file.cpp:16:5: error: anonymous structs are a GNU extension [-Werror,-Wgnu-anonymous-struct]
    struct {    // Function return value
    ^
source_file.cpp:28:9: error: designated initializers are a C99 feature [-Werror,-Wc99-extensions]
        .array = array_1,
        ^~~~~~~~~~~~~~~~
source_file.cpp:29:9: error: designated initializers are a C99 feature [-Werror,-Wc99-extensions]
        .size = ARRAY_COUNT(array_1),
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
source_file.cpp:24:16: warning: unused variable 'ret2' [-Wunused-variable]
    int  ret1, ret2;
               ^
source_file.cpp:27:13: warning: unused variable 'param' [-Wunused-variable]
    Param_u param = {
            ^
source_file.cpp:24:10: warning: unused variable 'ret1' [-Wunused-variable]
    int  ret1, ret2;
         ^
3 warnings and 4 errors generated.