C使用BinarySearch算法的函数(.bin文件)

2019年7月28日 198次阅读

我要创建一个函数来检查.bin文件中是否存在特定的单词.我想使用二进制搜索算法.事实是,我要从.bin文件中读取,所以我感到困惑(因为没有线,对吧？).功能对我不起作用.它表示“特定单词”(由用户输入)不存在,即使它确实存在.

你能帮忙的话,我会很高兴.

#include <iostream>
#include <string>
#include <fstream>
#include <cstring>
#include <algorithm>

using namespace std;
const int buffer_size = 30;

void Create_Bin_File ()
{
ifstream fin ("example.txt");  
ofstream fout ("Binary.bin", ios::binary); 
const unsigned int RECORD_SIZE = 30; // was BUFFER_SIZE
char buffer[RECORD_SIZE] = {0}; // zero init buffer

while (fin.getline (buffer, RECORD_SIZE))
{
fout.write (buffer, RECORD_SIZE);
// refill buffer with zeroes for next time round
fill_n (buffer, RECORD_SIZE, 0);
}
fin.close ();
fout.close ();
}

void Binary_Search (const string& filename, string SearchVal)
{
ifstream file (filename.c_str(), ios::binary);
if (file.is_open())
{
    cout << "The file is opened"<< endl;
    cout << "\n";
}
else
{
    cout << "Error opening file"<< endl;
    cout << "\n";
    return; // no point continuing Binary_Search() if file failed to open!
}
const unsigned int RECORD_SIZE = 30; // was BUFFER_SIZE
char buffer[RECORD_SIZE] = {0}; // zero init buffer
int recordCount  =  0;
int recordWanted = -1;
while (file.read(buffer, RECORD_SIZE))
{
    if(SearchVal == buffer)
    {

        recordWanted = recordCount;
        // if this was just a naive search loop could bail out now...
    }
    cout << recordCount << " : " << buffer << "\n";

    // refill buffer with zeroes for next time round
    fill_n (buffer, RECORD_SIZE, 0);
    ++recordCount;
}

cout << "\n";
cout << "file contains " << recordCount << " records\n";
cout << "\n";
if (recordWanted == -1)

    cout << "record wanted could not be found\n";
else

    cout << "record wanted is at index " << recordWanted << " records\n";
cout << "\n";
} 




int main()
{

Create_Bin_File();  
string word;
cout << "Enter word, that you want to find in a file: " << endl;
cin >> word;

Binary_Search("Binary.bin", word);


return 0;
}

任务：
“用C编写程序.如果程序使用文件,则不应将文件的全部内容复制到操作内存中.文件组件表示固定长度记录.
H7.编写一个程序,将所有标准C保留字放在一个有序表中(据我所知,有序表意味着这些单词按字母顺序排列).编写一个函数,使用二进制搜索检查输入字符串(长度为30)是否为C保留字.表应该作为直接访问文件. C保留程序应该从文本文件中读取.“

关于BinarySearch函数的grek40解决方案：

所以我做了记录功能：

std::string GetRecord(std::ifstream& inFile, int pos)
{
char buffer[RECORD_SIZE];
// clear possible flags like EOF, before moving the read position
inFile.clear();
// set the file read position to the requested record position
inFile.seekg(pos * RECORD_SIZE, std::ios::beg);
inFile.read(buffer, RECORD_SIZE);
// note: automatic conversion from char[] to std::string
return buffer;
}

和二进制搜索功能:(解决 – 工作！)

void Binary_Search (const string& filename, string SearchVal)
{
ifstream file (filename.c_str(), ios::binary);
if (file.is_open())
{
cout << "The file is opened"<< endl;
cout << "\n";
}
else
{
cout << "Error opening file"<< endl;
cout << "\n";
return; // no point continuing Binary_Search() if file failed to open!
}
int pos = 0;
int lowerLimit = 0;
int recordCount = 73; // Calculated before[I'll change this part, when I get      this function working]
                  // At this point, there's exactly 73 records in .bin file
 char buffer[RECORD_SIZE] = {0}; // zero init buffer (while loop will overwrite with record values)
 int upperLimit = recordCount;
 while ( (lowerLimit < upperLimit) ) // Searching as long as it doesn't find it
 {
    pos = (lowerLimit + upperLimit) / 2;
    std::string buffer = GetRecord(file, pos);

    if (buffer == SearchVal)
    {
        cout << "Found!";
        lowerLimit = 1; // For stopping (If found!)
        upperLimit = 0; // For stopping
    }
    else if (SearchVal > buffer)
    {
        lowerLimit = pos + 1;
    }
    else if (SearchVal < buffer)
    {
     upperLimit = pos;
    }

}
}

最佳答案 据我所知,你有一个解决方案,你可以将所有给定的单词从文本文件移动到二进制文件,如果它们存在,你可以在二进制文件中找到单词.

我想你创建了二进制文件,其长度等于(30),其中每个记录的文本部分都是零终止的.

现在,让我们创建一个函数,该函数接受打开的二进制文件流和记录位置,并返回该记录位置的字符串：

std::string GetRecord(std::ifstream& inFile, int pos)
{
    char buffer[RECORD_SIZE];
    // clear possible flags like EOF, before moving the read position
    inFile.clear();
    // set the file read position to the requested record position
    inFile.seekg(pos * RECORD_SIZE, std::ios::beg);
    inFile.read(buffer, RECORD_SIZE);
    // note: automatic conversion from char[] to std::string
    return buffer;
}

对于二进制搜索,您应该为搜索位置定义上限和下限.请注意,上限是lastItemPosition 1,因此您永远不会在基于零的索引中实际访问此位置.

int lowerLimit = 0;
int upperLimit = recordCount; // count when reading the lines in .txt

只要你没找到它就需要搜索结果并且lowerLimit< UPPERLIMIT. 您的下一个搜索词位于position =(lowerLimit upperLimit)/ 2;. 将单词与搜索文本进行比较.在平等方面,你已经完成了. 如果单词小于搜索文本,则结果位置可能比您刚看到的位置更高.所以你需要调整lowerLimit = position 1 如果单词大于搜索文本,则结果位置的索引值可能低于刚看到的值. upperLimit =位置 如上所述,使用调整后的上限和下限重复搜索.

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