[板子]快速读入

最新推荐文章于 2020-07-05 12:03:36 发布

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最新推荐文章于 2020-07-05 12:03:36 发布

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/Alessandro/p/9748291.html

本文详细介绍C++中实现快速输入输出的两种方法：使用getchar()和fread()。通过模板函数加速整数、浮点数及字符串的读取，适用于竞赛编程等对效率有高要求的场景。

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iostream

    ios::sync_with_stdio(false);
    cin.tie(0);
}

getchar() 版

// for Integers
template <class T> inline void read(T &x) {
    x = 0; int ch = getchar(), f = 0;
    while (ch < '0' || ch > '9') {
        if (ch == '-') f = 1;
        ch = getchar();
    }
    while (ch >='0' && ch <='9') {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    if (f) x = -x;
}

fread() 版

namespace fastIO{
    #define BUF_SIZE 100000
    #define OUT_SIZE 100000
    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';}
    template<class T> inline bool read(T &x){
        bool sign = 0; char ch = nc(); x = 0;
        for(; blank(ch); ch = nc());
        if(IOerror) return false;
        if(ch == '-') sign = 1, ch = nc();
        for(; ch >= '0' && ch <= '9'; ch = nc()) x = (x << 1) + (x << 3) + (ch ^ 48);
        if(sign) x = -x;
        return true;
    }
    inline bool read(double &x){
        bool sign = 0; char ch = nc(); x = 0;
        for(; blank(ch); ch = nc());
        if(IOerror) return false;
        if(ch == '-') sign = 1, ch = nc();
        for(; ch >= '0' && ch <= '9'; ch = nc()) x = x * 10.0 + (ch ^ 48);
        if(ch == '.') {
            double tmp = 1; ch = nc();
            for(; ch >= '0' && ch <= '9'; ch = nc()) tmp /= 10.0, x += tmp * (ch ^ 48);
        }
        if(sign) x = -x;
        return true;
    }
    inline bool read(char *s){
        char ch = nc();
        for(; blank(ch); ch = nc());
        if(IOerror) return false;
        for(; !blank(ch) && !IOerror; ch = nc()) *s++ = ch;
        *s = 0;
        return true;
    }
    template<class T,class... U>bool read(T& h,U&... t){return read(h)&&read(t...);}
    #undef OUT_SIZE
    #undef BUF_SIZE
}

using namespace fastIO;

注意: template<class T,class... U>bool read(T& h,U&... t){return read(h)&&read(t...);}是 c++11里规定的，考试时应该禁止使用

转载于:https://www.cnblogs.com/Alessandro/p/9748291.html