位集合矢量INT K掉用C

Question

界

我會究竟如何檢查一個bitset矢量給定的「項目」是否是出界

例如：

struct bitset { 
    unsigned char*vector; 
    int byteSize; 
    int bitSize; 
}; 
// create a new, empty bit vector set of 'size' items 
struct bitset * bitset_new(int size) { 
    struct bitset * theSet; 
    theSet = malloc(sizeof(struct bitset)); 
    theSet->vector = calloc(size, sizeof(char)); 
    theSet->bitSize = size; 
    theSet->byteSize= ((size/8) + 1); 
    return theSet; 
} 
    int bitset_find(struct bitset * this, int k) 
    { 
     int arrayIndex = k/8; 
     int indexPosition = k%8; 
     unsigned int flag = 1; // flag = 0000.....00001 

     flag = flag << indexPosition;  // flag = 0000...010...000 (shifted k positions) 

     if() 
     { 
     } 

    } 

究竟應該我在我的if語句中看看k是否不在我的向量中？

Answer 1

對於通常從位域檢查位，您可以使用按位運算符和&運算符。

您將不得不首先添加一些邏輯來確定您應該查看哪個字節vector。

這看起來是這樣的：

int bitset_find(struct bitset * this, int k) 
{ 
    int arrayIndex = k/8; 
    int indexPosition = k%8; 
    unsigned int flag = 1; // flag = 0000.....00001 

    flag = flag << indexPosition;  // flag = 0000...010...000 (shifted k positions) 


    // check to make sure arrayIndex is in range 
    if (arrayIndex > this->byteSize){ 
     return false; // out of range 
    } 

    char vector_byte = this->vector[arrayIndex]; 

    return vector_byte & flag; // return if the field from flag is found in the correct byte from the vector. 

}