动态地分配数组解释 [英] Dynamically allocating array explain
问题描述
这是示例code我的老师给我们看了关于如何动态地使用C分配一个数组？。但我不完全理解这一点。这里是code：
This is sample code my teacher showed us about "How to dynamically allocate an array in C?". But I don't fully understand this. Here is the code:
int k;
int** test;
printf("Enter a value for k: ");
scanf("%d", &k);
test = (int **)malloc(k * sizeof(int*));
for (i = 0; i < k; i++) {
test[i] = (int*)malloc(k * sizeof(int)); //Initialize all the values
}
我想在C，定义一个数组，你不得不把 [] 名称后，那么究竟是什么 INT **测试;是不是只是一个指针的指针？和的malloc（）行也确实迷惑了我.....
I thought in C, to define an array you had to put the [] after the name, so what exactly is int** test; isn't it just a pointer to a pointer? And the malloc() line is also really confusing me.....
推荐答案
据申报 INT **测试; ，测试是<一个href=\"http://stackoverflow.com/questions/18306935/need-of-pointer-to-pointer/18307020#18307020\">pointer到指针，在code PICE对于int值的矩阵分配内存使用动态malloc函数。
According to declaration int** test; , test is pointer to pointer, and the code pice allocating memory for a matrix of int values dynamically using malloc function.
声明：
test = (int **)malloc(k * sizeof(int*));
// ^^------^^-------
// allocate for k int* values
分配持续 K 指针为int的内存（为int * ）。因此，假设如果 K = 4 那么你得到这样的：
Allocate continue memory for k pointers to int (int*). So suppose if k = 4 then you gets something like:
temp 343 347 351 355
+----+ +----+----+----+----+
|343 |---►| ? | ? | ? | ? |
+----+ +----+----+----+----+
我假设地址是四个字节和？意味着垃圾值。
温度由malloc分配的变量返回地址的malloc中分配继续大小的内存块= K *的sizeof（INT **）这是在我的例子= 16个字节。
temp variable assigned returned address by malloc, malloc allocates continues memory blocks of size = k * sizeof(int**) that is in my example = 16 bytes.
在for循环您分配内存 K int和返回地址分配给温度[I] （位置$ p $的pviously分配的数组）。
In the for loop you allocate memory for k int and assign returned address to temp[i] (location of previously allocated array).
test[i] = (int*)malloc(k * sizeof(int)); //Initialize all the values
// ^^-----^^----------
// allocate for k int values
注：前pression 温度[I] == *（温度+ I）。
First malloc For loop
--------------- ------------------
temp
+-----+
| 343 |--+
+-----+ |
▼ 201 205 209 213
+--------+ +-----+-----+-----+-----+
343 | |= *(temp + 0) | ? | ? | ? | ? | //for i = 0
|temp[0] |-------| +-----+-----+-----+-----+
| 201 | +-----------▲
+--------+ 502 506 510 514
| | +-----+-----+-----+-----+
347 |temp[1] |= *(temp + 1) | ? | ? | ? | ? | //for i = 1
| 502 |-------| +-----+-----+-----+-----+
+--------+ +-----------▲
| | 43 48 52 56
351 | 43 | +-----+-----+-----+-----+
|temp[2] |= *(temp + 2) | ? | ? | ? | ? | //for i = 2
| |-------| +-----+-----+-----+-----+
+--------+ +-----------▲
355 | |
| 9002 | 9002 9006 9010 9014
|temp[3] | +-----+-----+-----+-----+
| |= *(temp + 3) | ? | ? | ? | ? | //for i = 3
+--------+ | +-----+-----+-----+-----+
+-----------▲
再次？意味着垃圾值。
其他景点：
1）你是由malloc铸造返回地址，但在C，你应该避免。阅读难道我投malloc的结果？刚操作如下：
1) You are casting returned address by malloc but in C you should avoid it. Read Do I cast the result of malloc? just do as follows:
test = malloc(k* sizeof(int*));
for (i = 0; i < k; i++){
test[i] = malloc(k * sizeof(int));
}
2）如果你是动态分配的内存，你需要释放内存明确，当你的工作与完成（释放动态分配的内存，你不能访问内存后）。步骤来释放内存测试将如下：
for (i = 0; i < k; i++){
free(test[i]);
}
free(test);
3）这是，如果你想完全分配的二维矩阵分配内存数组的数组的一种方式继续存储所有阵列检查这个答案：的分配内存二维数组中的函数C
4）如果描述可以帮助您想了解的3D分配入住这样的回答：<一href=\"http://stackoverflow.com/questions/16522035/allocate-memory-to-char-in-c/16522223#16522223\">Matrix字符串或/ 3D字符数组
4) If the description helps and you want to learn for 3D allocation Check this answer: Matrix of String or/ 3D char array
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