C语言 C 结构体中的数组
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Array in C struct
提问by Greg
I want to have two arrays in a struct, which are initialized at start but need editing further on. I need three instances of the struct, so that I can index into a specific struct and modify as I wish. Is it possible?
我想在一个结构中有两个数组，它们在开始时初始化但需要进一步编辑。我需要该结构的三个实例，以便我可以索引到特定的结构并根据需要进行修改。是否可以？
This is what I thought I could do but I get errors:
这是我认为我可以做但我得到错误：
struct potNumber{
int array[20] = {[0 ... 19] = 10};
char *theName[] = {"Half-and-Half", "Almond", "Rasberry", "Vanilla", …};
} aPot[3];
Then I access the structs as follows:
然后我按如下方式访问结构：
printf("some statement %s", aPot[0].array[0]);
aPot[0].theName[3];
…
回答by pmg
The struct themselves do not have data. You need to create objects of the struct type and set the objects ...
结构本身没有数据。您需要创建结构类型的对象并设置对象...
struct potNumber {
int array[20];
char *theName[42];
};
/* I like to separate the type definition from the object creation */
struct potNumber aPot[3];
/* with a C99 compiler you can use 'designated initializers' */
struct potNumber bPot = {{[7] = 7, [3] = -12}, {[4] = "four", [6] = "six"}};
for (i = 0; i < 20; i++) {
aPot[0].array[i] = i;
}
aPot[0].theName[0] = "Half-and-Half";
aPot[0].theName[1] = "Almond";
aPot[0].theName[2] = "Rasberry";
aPot[0].theName[3] = "Vanilla";
/* ... */
for (i = 0; i < 20; i++) {
aPot[2].array[i] = 42 + i;
}
aPot[2].theName[0] = "Half-and-Half";
aPot[2].theName[1] = "Almond";
aPot[2].theName[2] = "Rasberry";
aPot[2].theName[3] = "Vanilla";
/* ... */
回答by datenwolf
In C struct array elements must have a fixed size, so the char *theNames[]is not valid. Also you can not initialize a struct that way. In C arrays are static, i.e. one cannot change their size dynamically.
在 C 结构体数组元素必须有一个固定的大小，所以char *theNames[]是无效的。您也不能以这种方式初始化结构。在 C 中数组是静态的，即不能动态改变它们的大小。
A correct declaration of the struct would look like the following
结构的正确声明如下所示
struct potNumber{
int array[20];
char theName[10][20];
};
and you initialize it like this:
然后像这样初始化它：
struct potNumber aPot[3]=
{
/* 0 */
{
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10 /* up to 20 integer values*/ },
{"Half-and-Half", "Almond", "Raspberry", "Vanilla", /* up to 10 strings of max. 20 characters */ }
},
/* 1 */
{
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10 /* up to 20 integer values*/ },
{"Half-and-Half", "Almond", "Raspberry", "Vanilla", /* up to 10 strings of max. 20 characters */ }
},
/* 2 */
{
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10 /* up to 20 integer values*/ },
{"Half-and-Half", "Almond", "Raspberry", "Vanilla", /* up to 10 strings of max. 20 characters */ }
}
};
But, I'm pretty sure this is not what you want. The sane way to do this required some boilerplate code:
但是，我很确定这不是您想要的。这样做的明智方法需要一些样板代码：
struct IntArray
{
size_t elements;
int *data;
};
struct String
{
size_t length;
char *data;
};
struct StringArray
{
size_t elements;
struct String *data;
};
/* functions for convenient allocation, element access and copying of Arrays and Strings */
struct potNumber
{
struct IntArray array;
struct StringArray theNames;
};
Personally I strongly advise against using naked C arrays. Doing everything through helper structs and functions keeps you clear from buffer under/overruns and other trouble. Every serious C coder builds a substancial code library with stuff like this over time.
我个人强烈建议不要使用裸 C 数组。通过辅助结构和函数做所有事情可以让您远离缓冲区不足/溢出和其他问题。随着时间的推移，每个认真的 C 编码员都会用这样的东西构建一个实质性的代码库。
