动态结构的C动态数组

Question

我正在尝试创建动态结构的动态数组，但我无法使其正常工作。它会打印所有信息，但会出现 return 错误。如果我评论包含以下内容的行：

printf(" m[%i][%i] ID: %i VALUE: %f\n", i, j, m[i]->id, m[i]->values[j]);

编译成功，returns 0。我究竟做错了什么？我刚开始学习C，正在处理指针。

#include <stdio.h>
#include <stdlib.h>

typedef struct listDef{
   int id;
   float *values;
} ListSt;


int main()
{
    int max_fil, fil, col;
    max_fil = 4; /* Max 'ListSt' elements*/
    fil=2; /* Rows  */
    col=4; /* Columns */
    ListSt **m = NULL;
    int count = 0;
    int sizes[] = {4,6,8,10}; /* The sizes of each 4 elements to be created */
    m = (ListSt **)malloc(sizeof(int*)*max_fil); /* Assign a memory address for accesing 'm' (ListSt) */
    for(int i=0;i<fil;i++){
        m[i]->values = (float *)malloc(sizeof(float)*sizes[i]);
        m[i]->id = i;
        printf("-----------\n");
        printf("Element n.%i :\n\n", i);
        for(int j=0;j<sizes[i];j++){
            m[i]->values[j] = 0.1234*(i+1);
            /* If I comment the next line, it compiles OK. */
            printf(" m[%i][%i] ID: %i VALUE: %f\n", i, j, m[i]->id, m[i]->values[j]);

            int testint;
            float testfloat;
            testint = m[i]->id;
            testfloat = m[i]->values[j];
        }
    }

    free(m);
    return 0;
}

Answer 1

m 应该是 "pointer to ListSt" 类型，而不是 "pointer to pointer to ListSt".
您正在为指针数组分配内存：

m = (ListSt **)malloc(sizeof(int*)*max_fil);

...但数组中的元素仍未初始化。

顺便说一句，那应该是

sizeof (ListSt *) * (sizeof (sizes) / sizeof (* sizes))
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
size of an element number of elements in array "sizes"
然后您继续使用 m[0] 的值，但是 您从未将值分配给 m[0]。这叫做未定义行为；在这一点上，程序可以自由地做任何它想做的事，例如因分段错误而崩溃。

更具体地说，你说 m[i]->values =，但是 m[i] 是一个未初始化的变量，所以 m[i]-> 取消引用一个未初始化的指针。

Answer 2

好的。我想我有。如果有人可以检查它，那么对可能的错误或未来的问题或只是一些改进提出一些意见会很棒。

这是（修改后的）工作代码：

#include <stdio.h>
#include <stdlib.h>

typedef struct listDef{
   int id;
   float *values;
} ListSt;


int main()
{
    int max_fil, fil, col;
    max_fil = 4; /* Max 'ListSt' elements*/
    fil=4; /* Elements  */
    ListSt *m = NULL;
    int count = 0;
    int sizes[] = {4,6,8,10,12,13}; /* The sizes of each 4 elements to be created */
    m = (ListSt *)malloc(sizeof (ListSt) * fil); /* Assign a memory address for accesing 'm' (ListSt) */

    for(int i=0;i<fil;i++){
        m[i].values = (float *)malloc(sizeof(float)*sizes[i]);
        printf("-----------\n");
        printf("Element n.%i :\n\n", i);
        for(int j=0;j<sizes[i];j++){
            m[i].id = i;
            m[i].values[j] = 0.0001*(i+1)*(j+1);
            printf(" m[%i][%i] id: [%i] val: %f\n", i, j, m[i].id, m[i].values[j]);
        }
    }

    free(m);
    return 0;
}

并打印：

-----------
Element n.0 :

 m[0][0] id: [0] val: 0.000100
 m[0][1] id: [0] val: 0.000200
 m[0][2] id: [0] val: 0.000300
 m[0][3] id: [0] val: 0.000400
-----------
Element n.1 :

 m[1][0] id: [1] val: 0.000200
 m[1][1] id: [1] val: 0.000400
 m[1][2] id: [1] val: 0.000600
 m[1][3] id: [1] val: 0.000800
 m[1][4] id: [1] val: 0.001000
 m[1][5] id: [1] val: 0.001200
-----------
Element n.2 :

 m[2][0] id: [2] val: 0.000300
 m[2][1] id: [2] val: 0.000600
 m[2][2] id: [2] val: 0.000900
 m[2][3] id: [2] val: 0.001200
 m[2][4] id: [2] val: 0.001500
 m[2][5] id: [2] val: 0.001800
 m[2][6] id: [2] val: 0.002100
 m[2][7] id: [2] val: 0.002400
-----------
Element n.3 :

 m[3][0] id: [3] val: 0.000400
 m[3][1] id: [3] val: 0.000800
 m[3][2] id: [3] val: 0.001200
 m[3][3] id: [3] val: 0.001600
 m[3][4] id: [3] val: 0.002000
 m[3][5] id: [3] val: 0.002400
 m[3][6] id: [3] val: 0.002800
 m[3][7] id: [3] val: 0.003200
 m[3][8] id: [3] val: 0.003600
 m[3][9] id: [3] val: 0.004000

Process returned 0 (0x0)   execution time : 0.106 s
Press any key to continue.

Answer 3

我改线了：

return *m;

与：

return m[i];

它按预期工作！

Answer 4

最终的工作代码，如果它可以帮助某人：

#include <stdio.h>
#include <stdlib.h>

int max_fil, count;
typedef struct listDef{
   float *values;
   int id;
   int nElements;

} ListSt;



ListSt ListSt_init(ListSt *m, int i, int s){
    m[i].values = (float *)malloc(sizeof(float)*s);
    printf("-----------\n");
    printf("CREATE Element n.%i :\n\n", i);
    for(int j=0;j<s;j++){
        m[i].id = i;
        m[i].nElements = s;
        m[i].values[j] = 0.0000 + count*(0.1);
        printf("m[%i][%i]  ID: %i  TotalElements: %i  Value[%i]: %f\n", i, j, m[i].id, m[i].nElements, j, m[i].values[j]);
        count++;
    }

    return m[i];
}


int main()
{
    max_fil = 100; /* Max 'ListSt' elements addresses to be created */
    count = 0; /* Just a global counter for each 'values' */
    int sizes[] = {4,8,4}; /* The sizes of each 4 elements to be created */
    ListSt *m = NULL;
    m = (ListSt *)malloc(sizeof (ListSt) * max_fil); /* Assign a memory address for accesing 'm' (ListSt) */

    /* Lets create three lists */
    m[0] = ListSt_init(m, 0, sizes[0]);
    m[1] = ListSt_init(m, 1, sizes[1]);
    m[2] = ListSt_init(m, 2, sizes[2]);

    printf("\n-----------\n");
    printf("PRINT RESULT :\n");
    printf("-----------\n\n");
    /* Now we show the elements.... */
    for(int i=0;i<3;i++){
        printf("RESULT Element n.%i :\n\n", i);
        for(int j=0;j<sizes[i];j++){
            printf("m[%i][%i]  ID: %i  TotalElements: %i  Value[%i]: %f\n", i, j, m[i].id, m[i].nElements, j, m[i].values[j]);
        }
    }
    free(m);
    return 0;
}

动态结构的C动态数组

C dynamic array of dynamic struct

c

pointers

dynamic-arrays