类字段如何初始化？

发布于 2024-09-09 23:47:09 字数 634 浏览 8 评论 0原文

这是一个基本问题，但我很难找到明确的答案。

除了方法中的赋值之外，初始化器是否列出了 C++ 中初始化类字段的唯一方法？

如果我使用了错误的术语，这就是我的意思：

class Test
{
public:
    Test(): MyField(47) { }  // acceptable
    int MyField;
};

class Test
{
public:
    int MyField = 47; // invalid: only static const integral data members allowed
};

编辑：特别是，是否有一种很好的方法来使用结构初始值设定项来初始化结构字段？例如：

struct MyStruct { int Number, const char* Text };

MyStruct struct1 = {};  // acceptable: zeroed
MyStruct struct2 = { 47, "Blah" } // acceptable

class MyClass
{
    MyStruct struct3 = ???  // not acceptable
};

原文

A bit of a basic question, but I'm having difficulty tracking down a definitive answer.

Are initializer lists the only way to initialize class fields in C++, apart from assignment in methods?

In case I'm using the wrong terminology, here's what I mean:

class Test
{
public:
    Test(): MyField(47) { }  // acceptable
    int MyField;
};

class Test
{
public:
    int MyField = 47; // invalid: only static const integral data members allowed
};

EDIT: in particular, is there a nice way to initialize a struct field with a struct initializer? For example:

struct MyStruct { int Number, const char* Text };

MyStruct struct1 = {};  // acceptable: zeroed
MyStruct struct2 = { 47, "Blah" } // acceptable

class MyClass
{
    MyStruct struct3 = ???  // not acceptable
};

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雨轻弹 2024-09-16 23:47:09

在 C++x0 中，第二种方法也应该有效。

初始化列表是 C++ 中初始化类字段的唯一方法吗？

就您的编译器而言：是的。

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乙白 2024-09-16 23:47:09

静态成员可以以不同的方式初始化：

class Test {
    ....
    static int x;
};

int Test::x = 5;

我不知道你是否称其为“好”，但你可以相当干净地初始化结构成员，如下所示：

struct stype {
const char *str;
int val;
};

stype initialSVal = {
"hi",
7
};

class Test {
public:
    Test(): s(initialSVal) {}
    stype s;
};

Static members can be initialised differently:

class Test {
    ....
    static int x;
};

int Test::x = 5;

I don't know if you call this 'nice', but you can initialise struct members fairly cleanly like so:

struct stype {
const char *str;
int val;
};

stype initialSVal = {
"hi",
7
};

class Test {
public:
    Test(): s(initialSVal) {}
    stype s;
};

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守护在此方 2024-09-16 23:47:09

只是提一下，在某些情况下，您别无选择，只能使用初始值设定项列表在构造时设置成员的值：

class A
{
 private:

  int b;
  const int c;

 public:

 A() :
  b(1),
  c(1)
 {
  // Here you could also do:
  b = 1; // This would be a reassignation, not an initialization.
        // But not:
  c = 1; // You can't : c is a const member.
 }
};

Just to mention that in some cases, you have no choice but to use initializer lists to set a member's value on construction:

class A
{
 private:

  int b;
  const int c;

 public:

 A() :
  b(1),
  c(1)
 {
  // Here you could also do:
  b = 1; // This would be a reassignation, not an initialization.
        // But not:
  c = 1; // You can't : c is a const member.
 }
};

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