C语言 C 中结构的构造函数
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Constructor for structs in C
提问by Aillyn
Given:
鉴于：
struct objStruct {
int id;
int value;
};
typedef struct objStruct Object;
Is there a shortcut to allocate and initialize the object, something like a C++ constructor?
It could even be a preprocessor macro. Whatever makes the code shorter and more readable than this:
是否有分配和初始化对象的快捷方式，例如 C++ 构造函数？
它甚至可以是一个预处理器宏。无论什么使代码更短、更易读：
Object *newObj = malloc(sizeof(Object));
// successful allocation test snipped
newObj->id = id++;
newObj->value = myValue;
回答by JaredPar
In C I typically create a function in the style of a constructor which does this. For example (error checking omitted for brevity)
在 CI 中，通常会以构造函数的风格创建一个函数来执行此操作。例如（为简洁起见省略了错误检查）
Object* Object_new(int id, int value) {
Object* p = malloc(sizeof(Object));
p->id = id;
p->value = value;
return p;
}
...
Object* p1 = Object_new(id++, myValue);
回答by Jonathan Leffler
In C99 and beyond, you can use a compound literal, which looks like a cast followed by an initializer in braces:
在 C99 及更高版本中，您可以使用复合字面量，它看起来像一个强制转换，后跟一个大括号中的初始化程序：
int init_value = ...;
int init_id = ...;
Object newObj1 = (Object){ .value = init_value, .id = init_id };
Object newObj2 = (Object){ .id = init_id, .value = init_value };
The latter two lines achieve the same effect - the order of the fields is not critical. That is using 'designated initializers', another C99 feature. You can create a compound literal without using designated initializers.
后两行实现了相同的效果 - 字段的顺序并不重要。那就是使用“指定的初始值设定项”，这是另一个 C99 特性。您可以在不使用指定初始值设定项的情况下创建复合文字。
回答by grekhss
In C it is possible to declare an inline function with the same name as structure:
在 C 中，可以声明一个与结构同名的内联函数：
struct my
{
int a;
};
inline struct my* my(int* a)
{
return (struct my*)(a);
}
//somewhere in code
int num = 123;
struct my *sample = my(&num);
//somewhere in code
It looks pretty similar to C++ ctors.
它看起来与 C++ ctors 非常相似。
回答by nategoose
struct thingy {
char * label;
int x;
};
#define declare_thingy( name, label, val) struct thingy name = { label, val }
struct thingy * new_thingy(const char * label, int val) {
struct thingy * p = malloc(sizeof(struct thingy));
if (p) {
p->label = label;
p->val = val;
}
return p;
}
回答by Jens Gustedt
You really have to distinguish initialization of staticor autovariables and dynamic allocation on the head. For the first, do named initializers, for the second a well specified init function.
您确实必须在头上区分static或auto变量的初始化和动态分配。对于第一个，执行命名初始化程序，对于第二个，执行一个明确指定的 init 函数。
All that can be nicely
packed into macrosdo give you an easy static/autointialization and something similar to newin C++.
所有可以很好地
打包到宏中的东西确实可以为您提供简单的static/auto初始化和类似于newC++ 的东西。
回答by Tarantula
If you are looking for an object oriented "emulation" over C, I strongly recommend the GObject Type System [1], it's mature and largely used by GTK for instance.
如果您正在寻找一种基于 C 的面向对象的“仿真”，我强烈推荐 GObject 类型系统 [1]，例如，它已经成熟并被 GTK 大量使用。
GLib [2] has also a nice slice allocator for small objects, currently used by GNOME.
GLib [2] 也有一个很好的小对象切片分配器，目前由 GNOME 使用。
[1] GObject 参考手册
[2] GLib 内存片
