使用malloc为结构的多维数组 [英] using malloc for multidimensional array of struct
问题描述
这可能是一个基本的问题，但我想分配内存的结构的3维数组。
我想从文件中读取双打并希望在结构来存储。第一行是块号（因为这将是永远1这里不相关），第二行表示的x中网格点的数量，Y和Z分别坐标。在这种情况下，10个点在X，5在Y和1在Z方向上。而从第三行是X，Y，这是我想读双打每个点Z坐标。首先有所有的X分量（即10 * 5 * 1×坐标，然后类似地Y和Z）。文件格式是这样的：
This is probably a basic question but I want to allocate the memory for 3 dimensional array of a struct. I'm trying to read doubles from a file and want to store in struct. The first line is block number (not relevant here as it'll be 1 always), second line denotes the number of grid points in X, Y and Z coordinate respectively. In this case 10 points in X, 5 in Y and 1 in Z direction. And from third line, are the X,Y,Z coordinates of each points which are the doubles I would like to read. First there are all X components (i.e. 10*5*1 x coordinates, then similarly Y and Z). The file format is like this:
1
10 5 1
0.000000e+00 1.111111e+00 2.222222e+00 3.333333e+00
4.444445e+00 5.555555e+00 6.666667e+00 7.777778e+00
8.888889e+00 1.000000e+01 0.000000e+00 1.111111e+00
2.222222e+00 3.333333e+00 4.444445e+00 5.555555e+00
6.666667e+00 7.777778e+00 8.888889e+00 1.000000e+01
0.000000e+00 1.111111e+00 2.222222e+00 3.333333e+00
4.444445e+00 5.555555e+00 6.666667e+00 7.777778e+00
8.888889e+00 1.000000e+01 0.000000e+00 1.111111e+00
2.222222e+00 3.333333e+00 4.444445e+00 5.555555e+00
6.666667e+00 7.777778e+00 8.888889e+00 1.000000e+01
0.000000e+00 1.111111e+00 2.222222e+00 3.333333e+00
4.444445e+00 5.555555e+00 6.666667e+00 7.777778e+00
8.888889e+00 1.000000e+01...and so on...
我可以先读取4个整数，所以我知道我要存储的数据点的数量。然后我使用malloc函数分配内存和存储在变量中的数据。当我执行程序时，它读取整数，但无法读取双打。什么是我做错误？
I can read the first 4 integers and hence I know the number of points I wish to store data for. Then I'm using malloc function to allocate the memory and store the data in the variables. When I execute the program, it reads the integers but fails to read the doubles. What is the mistake I'm making?
下面是我的code：
#include <stdio.h>
#include <stdlib.h>
typedef struct{
double x,y,z;
}Mesh;
int main(void)
{
int nblocks, IMAX, JMAX, KMAX;
Mesh ***grid;
FILE *mesh = fopen("test.x","r");
fscanf(mesh,"%i %i %i %i",&nblocks,&IMAX,&JMAX,&KMAX);
printf("%i %i %i %i\n",nblocks,IMAX,JMAX,KMAX);
grid = malloc(sizeof(Mesh)*nblocks*IMAX*JMAX*KMAX);
fscanf(mesh,"%lf",&grid[0][0][0].x);
printf("%lf\n",grid[0][0][0].x);
fclose(mesh);
return 0;
}
在编译但开不读/写我存储在该结构的变量x变量的程序没有给出任何错误。 （如果一切正常，我可以把它放在循环，用于读取我没有在这里完成的所有值。）
The program doesn't give any error while compiling but it does't read/write the variable I stored in the x variable of the struct. (If this works, I can put it in loop for reading all values which I've not done here.)
如果我定义网格[IMAX] [JMAX] [KMAX] 后，我读 IMAX，JMAX，KMAX ，我得到正确的输出。但要知道这样的作品如何指针方式。
If I define Mesh grid[IMAX][JMAX][KMAX] after I read in IMAX,JMAX,KMAX, I get correct output. But wanted to know how pointer way of doing works.
感谢您，
Pranav
Thank you, Pranav
推荐答案
您有一个四维数组，而不是三个。的尺寸是：
You have a four dimensional array, not three. The dimensions are:
-
的nblocks -
IMAX -
JMAX -
KMAX
nblocksIMAXJMAXKMAX
因此，对于电网的类型必须是网格**** ，而不是网格*** 。
Hence, the type for grid has to be Mesh****, not Mesh***.
Mesh ****grid;
您code为电网分配内存必须是：
Your code to allocate memory for grid has to be:
grid = malloc(nblocks * (sizeof *grid));
for ( block = 0; block < nblocks; ++block )
{
grid[block] = malloc(IMAX * (sizeof *grid[0]));
for ( i = 0; i < IMAX ; ++i )
{
grid[block][i] = malloc(JMAX * (sizeof *grid[0][0]));
for ( j = 0; j < JMAX ; ++j )
{
grid[block][i][j] = malloc(KMAX * (sizeof *grid[0][0][0]));
}
}
}
现在，您可以使用访问网格数据：
Now, you can access the grid data using:
grid[block][index][jindex][kindex]
这是有效的用法：
These are valid usages:
fscanf(mesh,"%lf",&grid[0][0][0][0].x);
printf("%lf\n",grid[0][0][0][0].x);
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