Question

如何初始化变量大小的C ++结构＆＃34; StructB＆＃34;在下面声明：

#include <iostream>
#include <string>

typedef struct {
 char* a;
 int b;
} StructA;

typedef struct {
  StructA* pointers[];
  int pcount;
  int numbers[];
  int ncount;
} StructB;

int main()
{
    StructB *sb = new StructB; // I need 'sb' to be allocated in the heap
    sb->pcount = 5;
    sb->ncount = 3;
    sb->pointers = new StructA*[sb->pcount];
    sb->numbers = int[sb->ncount];
}

我遇到了这些编译错误。这些错误意味着什么，我该如何修复它们？谢谢你。

In function 'int main()': 
21:43: error: incompatible types in assignment of 'StructA**' to 'StructA* [0]' 
22:19: error: expected primary-expression before 'int' 
22:19: error: expected ';' before 'int'

Answer 1

听这不是很好的c ++方式，你在C ++环境下做C 如果它给你一些优势（IO，类型检查等）或学习，那就没关系。 C风格的动态内存分配完全是手动的。解除分配也是如此。由于您使用的是typedef，因此typedef可以使您和编译器更清楚。这是一个折磨的例子，我认为你想做什么。请注意，它已完成＆＃34; The Hard Way＆＃34;在这种情况下，这实际上是简单的方法 C ++中的C风格编码;

#include <iostream>
#include <string>


typedef struct {
char* a;
int b;
} StructA;


typedef StructA* A_p;   // A_p is "pointer to structA" (contains address of struct)                                                                           

typedef A_p* A_p_Array; // A_p_Array is "pointer to A_p"  (aka StructA**) contains address of A_p                                                             

typedef int* int_Array; // int_Array is "pointer to int" contains address of integer                                                                          


typedef struct {
 A_p_Array A_pointers;
 int pcount;
 int_Array numbers;
 int ncount;
} StructB;


int main()
{
 int i;

 StructA *sa = new StructA;

 StructB *sb = new StructB;

 sb->pcount = 5;
 sb->ncount = 3;

 A_p_Array  tmp_A_array;
 A_p        tmp;

 for ( i = 0 ; i < sb->pcount; i++)
 {
  tmp_A_array = new A_p; // create a StructA pointer                                                                                                      
  tmp = new StructA;     // create a StructA                                                                                                              
  tmp_A_array = &tmp;    // put address of tmp in mp_A_array                                                                                              
  tmp_A_array++;         // increment array address                                                                                                       
 }


 sb->A_pointers = tmp_A_array; // A_pointers now contains address of dynamically created array                                                               

 tmp_A_array = NULL;  // clear pointer but do NOT delete!                                                                                                    

 int_Array tmp_i_array;
 for ( i = 0 ; i < sb->ncount; i++)
 {
  tmp_i_array = new int(0); // c++ can create ints with initial values                                                                                    
  tmp_i_array++;
 }

 sb->numbers = tmp_i_array;
 tmp_i_array = NULL;  // clear pointer but do NOT delete!                                                                                                    


 /****** USE  Structs A & B    *****/

 // clean up the heap                                                                                                                                        

 A_p Ap;

 for ( i = 0 ; i < sb->pcount; i++)
 {
  Ap =  sb->A_pointers[i];
  delete Ap;  // each struct released separately
 }

 int* ip;
 for ( i = 0 ; i < sb->ncount; i++)
 {
  ip = & sb->numbers[i];
  delete ip;  //each int released separately
 }

 delete sb;

  return 0;
} // main

有更好的方法来做到这一点这是发明c ++和更高语言的一个原因。当你上课时，它会更容易一些但你可以遇到同样类型的问题所以得到指针和指针指向下来现在，以后会为你提供良好的服务。

如何初始化这个可变大小的结构？

1 个答案: