Question

我有一个结构变量，如下所示。（我已经更改了变量名，因此它们没有意义。）我在初始化myStruct1数组的位时遇到问题。

我需要初始化myStruct1.id.lengthOfData例如40和numberOfBits.number = 16。为此，我尝试使用memset等，但我不能正确地做到这一点。我怎么能这样做而不是手动做？提前谢谢。

#define unsigned int INT32U
typedef struct{
    struct{
        INT32U lengthOfData  :16;                       
        INT32U command   :8;                                                            
        INT32U sendBack  :1;                                
        INT32U backTest  :1;                                        
        INT32U required :1;                 
        INT32U reserved  :5;                                        
        INT32U student_class_id ;                      
    }id;
    union{
        INT32U number;
        struct{
            INT32U firstFiveBits:5;                          
            INT32U secondFiveBits:5;                        
            INT32U thirdFiveBits :5;                                                                                                                                                    INT32U eightBits :8;                        
            INT32U secondEightBits :8;                              
            INT32U restOfit:1;                          
        }numberOfbits;
    }foo;
    union{
        INT32U numberTwo;
        struct{
            INT16U firstSteenBits:16;
            INT16U secondSteenBits  :16;
        }bits;      
    }myUnion;
}myStruct1;

修改

这是我到目前为止所做的。

myStruct1 *myPtr;
    myPtr = new myStruct1;


    memset((myPtr), 0, sizeof(*myPtr)); // to zeros for all bits of myStruct1
    memset((myPtr), 3,1); // to give 3 to lengthOfData.

Answer 1

由于您正在处理位字段，您可以使用它们并将它们初始化为普通的struct字段

#include <iostream>
using namespace std;

#define INT32U unsigned int
#define INT16U unsigned short

typedef struct{
    struct{
        INT32U lengthOfData  :16;                       
        INT32U command   :8;                                                            
        INT32U sendBack  :1;                                
        INT32U backTest  :1;                                        
        INT32U required :1;                 
        INT32U reserved  :5;                                        
        INT32U student_class_id ;                      
    }id;
    union{
        INT32U number;
        struct{
            INT32U firstFiveBits:5;                          
            INT32U secondFiveBits:5;                        
            INT32U thirdFiveBits :5;                                                                                                                                                    INT32U eightBits :8;                        
            INT32U secondEightBits :8;                              
            INT32U restOfit:1;                          
        }numberOfbits;
    }foo;
    union{
        INT32U numberTwo;
        struct{
            INT16U firstSteenBits:16;
            INT16U secondSteenBits  :16;
        }bits;      
    }myUnion;
}myStruct1;

int main() {
    myStruct1 obj;
    obj.id.required = 1; // Make sure not to exceed the bit capacity
    obj.id.lengthOfData = 22; // Make sure not to exceed the bit capacity
    cout << obj.id.lengthOfData << endl;
    cout << obj.id.required << endl;
    obj.id.required = 0;
    cout << obj.id.required << endl;

    return 0;
}

http://ideone.com/PUSp1h

请确保不要超过位字段本身的容量，并且不要依赖字段的顺序为单个机器字

初始化包含其他结构C ++的结构位

1 个答案: