Question

我要创建一个检查.bin文件中是否存在特定单词的函数。我想使用二进制搜索算法。事情是，我从.bin文件中读取，所以我感到困惑（因为没有线路，对吧？）。功能对我不起作用。它说＆＃39;具体的词＆＃39; （由用户输入）不存在，即使它确实存在。任何帮助都会很好。

#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;
}

TASK：＆＃34;用C ++编写程序。如果程序使用文件，则不应将文件的整个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。＆＃34;

关于BinarySearch函数的grek40解决方案：

所以我创建了记录功能：

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;
}

二进制搜索功能:(已解决 - 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;
    }

}
}

Answer 1

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），每条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：

for (i = 0; i < buf.length; i++) {
  const byte = buf[i];
  const hexChar = byte.toString(16); // convert the decimal `byte` to hex string;
  // do something with hexChar, e.g. console.log(hexChar);
}

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，上限为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; }，因此您永远不会在基于零的索引中实际访问此位置。

lastItemPosition + 1

只要您找不到结果并int lowerLimit = 0; int upperLimit = recordCount; // count when reading the lines in .txt，就需要搜索结果。

您的下一个搜索字词位于lowerLimit < upperLimit。

将该字词与搜索文字进行比较。在平等方面，你已经完成了。

如果单词小于搜索文本，则结果位置可以是高指数，而不是您刚刚查看的指数。因此，您需要调整position = (lowerLimit + upperLimit) / 2;

如果单词大于搜索文本，则结果位置可以是较低索引，而不是您刚刚查看的位置。 lowerLimit = position + 1

如上所述，您可以使用调整后的上限和下限重复搜索。

C ++使用BinarySearch算法的函数（.bin文件）

1 个答案: