输入输出挂

关于输入挂

输入速度：getchar > scanf > cin

特点：快糙猛？

探索输入挂

预备工作

随机产生一百万个整型数，写入指定文件里

#include <ctime>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    srand(time(NULL));
    freopen("00out.txt", "w", stdout);
    int n;
    int num = 1000000;
    while(num--)
    {
        n = rand() % 1000;
        cout << n << ' ';
    }
    return 0;
}

开始探索

分别用输入挂（getchar）、scanf、cin读入一百万个整型数字，看运行时间

#include <ctime>
#include <cstdio>
#include <iostream>
using namespace std;
const int N = 1000005;
int a[N];
int b[N];

int Scan()     ///输入外挂
{
    int res = 0, ch ,flag = 0;
    if( (ch = getchar()) == '-' )
        flag = 1;
    else if(ch >= '0' && ch <= '9')
        res = ch - '0';
    while((ch = getchar()) >= '0' && ch <= '9')
        res = res * 10 + ch - '0';
    return flag ? -res : res;
}
void Out(int a)    ///输出外挂
{
    if(a < 0)
    {
        putchar('-');
        a *= -1;
    }
    if(a > 9)
        Out(a / 10);
    putchar(a % 10 + '0');
}

int main()
{
    clock_t start, over;
    double  duration;

    freopen("00out.txt", "r", stdin);
    start = clock();
    for(int i = 0; i < 1000000; ++i)
        a[i] = Scan();
    over = clock();
    duration = double(over - start) / CLOCKS_PER_SEC;
    cout << duration << " (s)" << '\n';
    fclose(stdin);

    freopen("00out.txt", "r", stdin);
    start = clock();
    for(int i = 0; i < 1000000; ++i)
        scanf("%d", &a[i]);
    over = clock();
    duration = double(over - start) / CLOCKS_PER_SEC;
    cout << duration << " (s)" << '\n';
    fclose(stdin);

    freopen("00out.txt", "r", stdin);
    start = clock();
    for(int i = 0; i < 1000000; ++i)
        cin >> a[i];
    over = clock();
    duration = double(over - start) / CLOCKS_PER_SEC;
    cout << duration << " (s)" << '\n';
    fclose(stdin);
}

结果

读入挂(getchar) —— 33ms

scanf —— 136ms

cin —— 1412ms

关于double的读入挂（一般用不到）

#include <cstdio>
#include <iomanip>
#include <iostream>
#include <algorithm>
using namespace std;

double Scan()
{
    int ch, pos = 1, num = 0;///num为字符串总长度，pos为小数点排第几位
    double res = 0;
    bool flag = 0, found = 0;

    if( (ch = getchar()) == '-' )
        flag = 1;
    else if(ch >= '0' && ch <= '9')
        res = ch - '0';
    num++;

    while((ch = getchar()) >= '0' && ch <= '9' || ch == '.')
        {
            num++;
            if(ch == '.')
            {
                found = 1;
                pos++;
            }
            else
            {
                res = res * 10 + ch - '0';
                if(!found)
                    pos++;
            }
        }
    res *= pow(0.1, num - pos);
    return flag ? -res  : res ;
}

int main()
{
    double ans;
    while(ans = Scan())
    {
        cout << fixed << std::setprecision(10) << ans << '\n';
    }
    return 0;
}

注意事项

scanf("%d", &n);
getchar();
for(int i = 0; i < n; ++i)
    a[i] = Scan();

中间的getchar()不加上可能输出测试时表面上看没影响，但就是会WA！