英文:
How to properly use brace enclosed initiator?
问题
I have defined 3 nested structs in my project and want to create a default setup that is used by many functions. I have tried using the following code which the IDE says should work.
struct xBitValue {
size_t depth=0;
uint64_t key=1;
//allow comparison
bool operator==(const xBitValue& b) const {
return ((depth==b.depth) && (key==b.key));
}
bool operator!=(const xBitValue& b) const {
return ((depth!=b.depth) || (key!=b.key));
}
};
struct stringHeaderOption {
xBitValue header;
size_t encoder=0;
};
struct stringHeaderOptions {
size_t xBitLength;
std::vector<stringHeaderOption> options;
};
const stringHeaderOptions defaultHeaderOptions={2,{
{{0,1},0},
{{0,2},1},
{{0,3},2},
{{1,1},3}
}};
but I get the error could not convert {{{0, 1}, 0}, {{0, 2}, 1}, {{0, 3}, 2}, {{1, 1}, 3}} from <brace-enclosed initializer list> to std::vector<stringHeaderOption> with an error pointing to the last }.
It seems there is something I am missing on how to initialize values in this way.
C++11
英文:
I have defined 3 nested structs in my project and want to create a default setup that is used by many functions. I have tried using the following code which the IDE says should work.
struct xBitValue {
size_t depth=0;
uint64_t key=1;
//allow comparison
bool operator==(const xBitValue& b) const {
return ((depth==b.depth) && (key==b.key));
}
bool operator!=(const xBitValue& b) const {
return ((depth!=b.depth) || (key!=b.key));
}
};
struct stringHeaderOption {
xBitValue header;
size_t encoder=0;
};
struct stringHeaderOptions {
size_t xBitLength;
std::vector<stringHeaderOption> options;
};
const stringHeaderOptions defaultHeaderOptions={2,{
{{0,1},0},
{{0,2},1},
{{0,3},2},
{{1,1},3}
}};
but I get the error could not convert {{{0, 1}, 0}, {{0, 2}, 1}, {{0, 3}, 2}, {{1, 1}, 3}} from <brace-enclosed initializer list> to std::vector<stringHeaderOption> with an error pointing to the last }.
It seems there is something I am missing on how to initialize values in this way.
C++11
答案1
得分: 3
你的目标是进行聚合初始化。然而，在C++11中，聚合类型不能具有默认成员初始化器 - 这在C++14中已更改（参见：https://en.cppreference.com/w/cpp/language/aggregate_initialization#Definitions）
你的代码在C++14及更高版本中编译通过。在C++11中，它将无法工作；
在C++11中，如果删除对xBitValue和stringHeaderOption的数据成员提供的默认值，它将编译通过。
请参见：http://coliru.stacked-crooked.com/a/eb49bcb837a45f89
**注意：**在C++14及更高版本中，以下代码可以编译通过（在C++11中将导致错误）：
stringHeaderOption s1{1,0,1};
stringHeaderOption s2{1,0};
stringHeaderOption s3{1};
因此，也许你只想允许创建你认为合法的结构的构造函数。
英文:
You are aiming for an aggregate initialization.
However, In C++11 an aggregate cannot have default member initializers - this was changed in C++14 (See: https://en.cppreference.com/w/cpp/language/aggregate_initialization#Definitions)
Your code compiles in C++14 and later. It will not work in C++11;
See it compile in C++14: http://coliru.stacked-crooked.com/a/8484258abc2e02d6
It will compile in C++11 if you remove the default values you are giving to the data members of xBitValue and stringHeaderOption.
See: http://coliru.stacked-crooked.com/a/eb49bcb837a45f89
Note: In C++14 and later the following compiles (in C++11 it will result in an error):
stringHeaderOption s1{1,0,1};
stringHeaderOption s2{1,0};
stringHeaderOption s3{1};
Therefore, perhaps you would like to only allow constructors that create structs you find legal.
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