Fast IO 的探索及模板，竞赛专用。

其他 2019-01-20 10:51:04 阅读次数: 0
版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_40727946/article/details/81675026

竞赛专用~~~

通过测试一千万个数据的读入，来判断何种方法最快。每种测试结果都有时间附上。

首先生成一千万个随机数

#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("Date.txt","w",stdout);
	srand((unsigned)time(NULL));
	for(int i=0;i<10000000;i++)
	{
		int n=rand();
		cout<<n<<endl;
	}
	return 0;
}

生成的文件大小为 63.5 MB

1.用C++中最简单的cout来读入，并且不关闭同步，时间为：4.673 s

#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("Date.txt","r",stdin);
	//std::ios::sync_with_stdio(false);
	for(int i=0;i<10000000;i++)
	{
		int a;
		cin>>a;
	} 
    printf("%.3f",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}

2.用scanf来读入，时间为：1.626 s

在竞赛的时候，有人习惯把万能头上面再添加一个 stdio ，似乎可以增加速度，我刚刚测试的时候并没发现可以加快读入速度。

#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("Date.txt","r",stdin);
	for(int i=0;i<10000000;i++)
	{
		int a;
		scanf("%d",&a);
	}
    printf("%.3f",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}

3.关闭同步后用cin读入文件，时间为：1.309

#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("Date.txt","r",stdin);
	std::ios::sync_with_stdio(false);
	for(int i=0;i<10000000;i++)
	{
		int a;
		cin>>a;
	}
    printf("%.3f",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}

4.手写read来读入文件，时间为：0.606 s

#include<bits/stdc++.h>
using namespace std;

inline void read(int &X)
{
    X=0;int w=0;char ch=0;
    while(!isdigit(ch))w|=ch=='-',ch=getchar();
    while( isdigit(ch))X=(X<<3)+(X<<1)+(ch^48),ch=getchar();
    X=w?-X:X;
}

int main()
{
	freopen("Date.txt","r",stdin);
	for(int i=0;i<10000000;i++)
	{
		int a;
		read(a);
	}
    printf("%.3f",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}

5.fread->read，时间为：0.507 s

#include<stdio.h>
#include<bits/stdc++.h>
using namespace std;

namespace fastIO {
#define BUF_SIZE 100000
    //fread -> read
    bool IOerror = 0;
    inline char nc() {
        static char buf[BUF_SIZE], *p1 = buf + BUF_SIZE, *pend = buf + BUF_SIZE;
        if (p1 == pend) {
            p1 = buf;
            pend = buf + fread(buf, 1, BUF_SIZE, stdin);
            if (pend == p1) {
                IOerror = 1;
                return -1;
            }
        }
        return *p1++;
    }
    inline bool blank(char ch) {
        return ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t';
    }
    inline void read(int &x) {
        char ch;
        while (blank(ch = nc()));
        if (IOerror) return;
        for (x = ch - '0'; (ch = nc()) >= '0' && ch <= '9'; x = x * 10 + ch - '0');
    }
#undef BUF_SIZE
};
using namespace fastIO;


int main()
{
	freopen("Date.txt","r",stdin);
	for(int i=0;i<10000000;i++)
	{
		int a;
		read(a);
	}
    printf("%.3f",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}

总之，经过这些快速读入的方法，发现还是有很大的区别的。以后要多加注意~~~

https://blog.csdn.net/shifuwawa/article/details/5811397

https://blog.csdn.net/draven__/article/details/77530672

分享一个好东西，嘿嘿~~，快速读入输出各种包含 long long , double , char , 以及一串字符的快读模板。

模板

模板

模板

namespace fastIO{
    #define BUF_SIZE 100000
    #define OUT_SIZE 100000
    #define ll long long
    //fread->read
    bool IOerror=0;
    inline char nc(){
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if (p1==pend){
            p1=buf; pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if (pend==p1){IOerror=1;return -1;}
            //{printf("IO error!\n");system("pause");for (;;);exit(0);}
        }
        return *p1++;
    }
    inline bool blank(char ch){return ch==' '||ch=='\n'||ch=='\r'||ch=='\t';}
    inline void read(int &x){
        bool sign=0; char ch=nc(); x=0;
        for (;blank(ch);ch=nc());
        if (IOerror)return;
        if (ch=='-')sign=1,ch=nc();
        for (;ch>='0'&&ch<='9';ch=nc())x=x*10+ch-'0';
        if (sign)x=-x;
    }
    inline void read(ll &x){
        bool sign=0; char ch=nc(); x=0;
        for (;blank(ch);ch=nc());
        if (IOerror)return;
        if (ch=='-')sign=1,ch=nc();
        for (;ch>='0'&&ch<='9';ch=nc())x=x*10+ch-'0';
        if (sign)x=-x;
    }
    inline void read(double &x){
        bool sign=0; char ch=nc(); x=0;
        for (;blank(ch);ch=nc());
        if (IOerror)return;
        if (ch=='-')sign=1,ch=nc();
        for (;ch>='0'&&ch<='9';ch=nc())x=x*10+ch-'0';
        if (ch=='.'){
            double tmp=1; ch=nc();
            for (;ch>='0'&&ch<='9';ch=nc())tmp/=10.0,x+=tmp*(ch-'0');
        }
        if (sign)x=-x;
    }
    inline void read(char *s){
        char ch=nc();
        for (;blank(ch);ch=nc());
        if (IOerror)return;
        for (;!blank(ch)&&!IOerror;ch=nc())*s++=ch;
        *s=0;
    }
    inline void read(char &c){
        for (c=nc();blank(c);c=nc());
        if (IOerror){c=-1;return;}
    }
    //fwrite->write
    struct Ostream_fwrite{
        char *buf,*p1,*pend;
        Ostream_fwrite(){buf=new char[BUF_SIZE];p1=buf;pend=buf+BUF_SIZE;}
        void out(char ch){
            if (p1==pend){
                fwrite(buf,1,BUF_SIZE,stdout);p1=buf;
            }
            *p1++=ch;
        }
        void print(int x){
            static char s[15],*s1;s1=s;
            if (!x)*s1++='0';if (x<0)out('-'),x=-x;
            while(x)*s1++=x%10+'0',x/=10;
            while(s1--!=s)out(*s1);
        }
        void println(int x){
            static char s[15],*s1;s1=s;
            if (!x)*s1++='0';if (x<0)out('-'),x=-x;
            while(x)*s1++=x%10+'0',x/=10;
            while(s1--!=s)out(*s1); out('\n');
        }
        void print(ll x){
            static char s[25],*s1;s1=s;
            if (!x)*s1++='0';if (x<0)out('-'),x=-x;
            while(x)*s1++=x%10+'0',x/=10;
            while(s1--!=s)out(*s1);
        }
        void println(ll x){
            static char s[25],*s1;s1=s;
            if (!x)*s1++='0';if (x<0)out('-'),x=-x;
            while(x)*s1++=x%10+'0',x/=10;
            while(s1--!=s)out(*s1); out('\n');
        }
        void print(double x,int y){
            static ll mul[]={1,10,100,1000,10000,100000,1000000,10000000,100000000,
                1000000000,10000000000LL,100000000000LL,1000000000000LL,10000000000000LL,
                100000000000000LL,1000000000000000LL,10000000000000000LL,100000000000000000LL};
            if (x<-1e-12)out('-'),x=-x;x*=mul[y];
            ll x1=(ll)floor(x); if (x-floor(x)>=0.5)++x1;
            ll x2=x1/mul[y],x3=x1-x2*mul[y]; print(x2);
            if (y>0){out('.'); for (size_t i=1;i<y&&x3*mul[i]<mul[y];out('0'),++i); print(x3);}
        }
        void println(double x,int y){print(x,y);out('\n');}
        void print(char *s){while (*s)out(*s++);}
        void println(char *s){while (*s)out(*s++);out('\n');}
        void flush(){if (p1!=buf){fwrite(buf,1,p1-buf,stdout);p1=buf;}}
        ~Ostream_fwrite(){flush();}
    }Ostream;
    inline void print(int x){Ostream.print(x);}
    inline void println(int x){Ostream.println(x);}
    inline void print(char x){Ostream.out(x);}
    inline void println(char x){Ostream.out(x);Ostream.out('\n');}
    inline void print(ll x){Ostream.print(x);}
    inline void println(ll x){Ostream.println(x);}
    inline void print(double x,int y){Ostream.print(x,y);}	//y为小数点后几位
    inline void println(double x,int y){Ostream.println(x,y);}
    inline void print(char *s){Ostream.print(s);}
    inline void println(char *s){Ostream.println(s);}
    inline void println(){Ostream.out('\n');}
    inline void flush(){Ostream.flush();}			//清空
    #undef ll
    #undef OUT_SIZE
    #undef BUF_SIZE
};
using namespace fastIO;

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