Быстрое чтение файла

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
using namespace std;
 
int main()
{
    double val;
    cout<<"Enter num of elements : ";
    long num;cin>>num;
    ofstream ofs("file.txt");
    ofs<<num<<endl;
    srand(time(0));
    for(long i = 0; i < num; i++)
    {
        cout<<(val = rand()%(2*num)/(1.0 + rand()%2));
        ofs<<val;
        if(i != num - 1)
        {
            cout<<" ";
            ofs<<" ";
        }
        else
            cout<<"\n";
    }
    ofs.close();
    system("pause");
    return 0;
}

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
using namespace std;
double * parse_fscanf(long &n, double * arr);
double * parse_strtok(long &n, double * arr);
double * parse_ifstrm(long &n, double * arr);
 
int main()
{
    long n,bgn,end;
    double * arr = NULL;
    cout<<"\tVariant C(fscanf)\n";
    time(&bgn);
    cout<<"Algorithm started at : "<<asctime(localtime(&bgn));
    arr = parse_fscanf(n, arr);
    time(&end);
    cout<<"Algorithm stoped at : "<<asctime(localtime(&end));
    cout<<"Time of work : "<<difftime(end,bgn)<<" sec"<<endl;
    cout<<"arr["<<0<<"] = "<<arr[0]<<endl;
    cout<<"arr["<<n - 1<<"] = "<<arr[n - 1]<<endl;
    delete [] arr;
 
    cout<<"\tVariant C(strtok)\n";
    time(&bgn);
    cout<<"Algorithm started at : "<<asctime(localtime(&bgn));
    arr = parse_strtok(n, arr);
    time(&end);
    cout<<"Algorithm stoped at : "<<asctime(localtime(&end));
    cout<<"Time of work : "<<difftime(end,bgn)<<" sec"<<endl;
    cout<<"arr["<<0<<"] = "<<arr[0]<<endl;
    cout<<"arr["<<n - 1<<"] = "<<arr[n - 1]<<endl;
    delete [] arr;
 
    cout<<"\tVariant C++(ifstream)\n";
    time(&bgn);
    cout<<"Algorithm started at : "<<asctime(localtime(&bgn));
    arr = parse_ifstrm(n, arr);
    time(&end);
    cout<<"Algorithm stoped at : "<<asctime(localtime(&end));
    cout<<"Time of work : "<<difftime(end,bgn)<<" sec"<<endl;
    cout<<"arr["<<0<<"] = "<<arr[0]<<endl;
    cout<<"arr["<<n - 1<<"] = "<<arr[n - 1]<<endl;
    delete [] arr;
 
    system("pause");
    return 0;
}
 
double * parse_fscanf(long &n, double * arr)
{
    FILE * file = fopen("file.txt","rb");
    if(!file)
        cout<<"Error open file.txt\n";
    else
    {
        fscanf(file,"%u",&n);
        arr = new double[n];
        for(long i = 0; i < n; i++)
            fscanf(file,"%lf",&arr[i]);
        fclose(file);
    }
    return arr;
}
 
double * parse_strtok(long &n, double * arr)
{
    char * tok;
    char * str;
    char delim[] = " \n";
    long i,sLen;
    FILE * file = fopen("file.txt","rb");
    if(!file)
        cout<<"Error open file.txt\n";
    else
    {
        fseek(file,0,SEEK_END);
        sLen = ftell(file);
        fseek(file,0,SEEK_SET);
        if(!(str = (char *)malloc(sizeof(char)*(sLen + 1))))
            cout<<"Allocation memory error\n";
        else
        {
            fread(str,1,sLen,file);
            str[sLen] = '\0';
        }
        fclose(file);
        if(str)
        {
            
            tok = strtok(str,delim);
            n = atoi(tok);i = 0;
            arr = new double[n];
            tok = strtok(NULL,delim);
            while(tok)
            {
                arr[i++] = atof(tok);
                tok = strtok(NULL,delim);
            }
        }
    }
    return arr;
}
 
double * parse_ifstrm(long &n, double * arr)
{
    ifstream ifs("file.txt");
    if(!ifs)
        cout<<"Error open file.txt\n";
    else
    {
        ifs>>n;
        arr = new double[n];
        for(long i = 0; i < n && !ifs.eof(); i++)
            ifs>>arr[i];
        ifs.close();
    }
    return arr;
}