Question

#include <fstream>
#include <iostream>

using namespace std;

bool find_in_file(char*);
void insert_in_file(char*);
inline bool isNull(char* word);

int main()
{
    char word[25];

    for(int i = 0; i < 10; i++)
    {
        cin >> word;

        if( find_in_file(word) )
            cout << "found" << endl;
        else
            insert_in_file(word);
    }
    system("pause");
}

bool find_in_file(char* word)
{
    ifstream file;
    file.open("file.dat", ios::in);
    char contents[655][25] = {0};


    file.read(reinterpret_cast<char*>(contents), 16*1024);
    file.close();

    int i = 0;

    while( !isNull(contents[i]) )
    {
        if( strcmp(contents[i], word) == 0)
            return true;

        if( strcmp(contents[i], word) < 0 )
            i = 2*i + 2;
        else
            i = 2*i + 1;
    }

    return false;
}

void insert_in_file(char* word)
{
    fstream file;
    file.open("file.dat", ios::in | ios::binary);
    char contents[655][25] = {0};

    file.read(reinterpret_cast<char*>(contents), 16*1024);
    file.close();


    file.open("file.dat", ios::in | ios::out | ios::binary);

    if( isNull(contents[0]) )
    {
        file.write(word, 25);
        file.close();
        return;
    }

    int parent;
    int current = 0;

    while( !isNull(contents[current]) )
    {
        parent = current;

        if( strcmp( contents[current], word ) < 0 )
            current = current*2 + 2;
        else if ( strcmp( contents[current], word ) > 0)
            current = current*2 + 1;
        else
            return;
    }

    int insertAt;

    if( strcmp(contents[parent], word ) < 0 )
        insertAt = parent*2 + 2;
    else
        insertAt = parent*2 + 1;

    file.seekp(insertAt*25, ios_base::beg);
    file.write(reinterpret_cast<const char*>(word), 25);
    file.close();
}

inline bool isNull(char* word)
{
    return word[0] == 0;
}

The above code implements a binary search tree on file. It uses char arrays of length 25 as nodes. It assumes a size of around 16K as max for the file. The tree is stored in this format:

0 root
1 left child of root - L
2 right child of root - R
3 left child of L - LL
4 right child of L - LR
5 left child of R - RL
6 right child of R - RR

and so on. In the absence of a child, an empty node is inserted. Now I have to do the same thing in PHP. How is it possible since as far as I know, PHP does not provide binary file access. Eagerly looking forward to your responses 🙂

edit: If I write an integer to file in binary mode, c/c++ will write 4 bytes regardless of the value stored in that integer. PHP will write the plain integer value in file, that is, 0 if the value is 0 and 100 if it is 100. This raises problems when using seek because I dont know the specific number of bytes to move the put pointer. Or in this case, I am writing character arrays of fixed length = 25. How can I do this in php since the variables dont have a type at all?

Answer 1

PHP does provide binary file access. Use fopen() and specify 'b' in the mode field.

To perform random access (i.e. read/write), you should specify 'r+' in the mode field (or 'w+', 'x+' or 'a+', depending on precisely what you want to do).

To actually write binary data (rather than textual representations of that data), use fwrite() and pack().