快读详解 —— 从原理到优化#

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#include <iostream>
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int main() {
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    std::ios::sync_with_stdio(false);
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    std::cin.tie(nullptr);
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    int a;
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    std::cin >> a;
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    std::cout << a << '\n';
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}

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int a;
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scanf("%d", &a);
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printf("%d", a);

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#include <cctype>
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#ifdef __unix__
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  #define gc getchar_unlocked
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  #define pc putchar_unlocked
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#else
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  #define gc _getchar_nolock
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  #define pc _putchar_nolock
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#endif
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namespace IOPlus {
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    inline int read() {
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        int x = 0, f = 1;
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        char ch = gc();
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        while (!isdigit(ch))f = (ch == '-') ? -1 : 1,              ch = gc();
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        while ( isdigit(ch))x = (x << 1) + (x << 3) + (ch ^ 48),   ch = gc();
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        return f * x;
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    }
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    inline void fwrites(int x, char split = '\n') {
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        if (x < 0) {
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            pc('-');
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            x = -x;
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        }
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        static char buf[40];
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        int cnt = 0;
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        do {
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            buf[cnt++] = x % 10 + '0';
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            x /= 10;
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        } while (x);
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        while (cnt--)pc(buf[cnt]);
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        pc(split);
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    }
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    template<typename T>
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    void write(T& x) {
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        cout << x << '\n';
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    }
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    template<typename T, typename... Args>
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    void write(T& x, Args&... rest) {
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        cout << x << ' ';
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        write(rest...);
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    }
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} using namespace IOPlus;

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#include <cctype>
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#include <cstdio>
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    namespace FastIO
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{
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    const int BUF_SIZE = 1 << 20;
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    char in_buf[BUF_SIZE], *in_p1 = in_buf, *in_p2 = in_buf;
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    char out_buf[BUF_SIZE], *out_p = out_buf;
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    inline char gc()
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    {
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        if (in_p1 == in_p2)
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        {
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            in_p2 = (in_p1 = in_buf) + fread(in_buf, 1, BUF_SIZE, stdin);
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            if (in_p1 == in_p2)
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                return EOF;
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        }
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        return *in_p1++;
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    }
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    template <typename T>
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    inline bool read(T & x)
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    {
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        x = 0;
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        int f = 1;
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        char ch = gc();
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        while (!isdigit(ch))
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        {
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            if (ch == EOF)
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                return false; // EOF 返回 false
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            if (ch == '-')
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                f = -1;
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            ch = gc();
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        }
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        while (isdigit(ch))
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        {
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            x = x * 10 + (ch - '0');
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            ch = gc();
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        }
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        x *= f;
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        return true; // 成功读取
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    }
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    inline void flush()
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    {
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        if (out_p != out_buf)
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        {
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            fwrite(out_buf, 1, out_p - out_buf, stdout);
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            out_p = out_buf;
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        }
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    }
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    inline void push(char c)
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    {
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        if (out_p - out_buf == BUF_SIZE)
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            flush();
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        *out_p++ = c;
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    }
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    template <typename T>
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    inline void write(T x)
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    {
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        if (x < 0)
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        {
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            push('-');
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            x = -x;
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        }
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        char sta[20];
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        int top = 0;
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        do
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        {
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            sta[top++] = x % 10;
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            x /= 10;
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        } while (x);
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        while (top--)
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            push(sta[top] + '0');
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    }
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    template <typename T>
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    inline void writeln(T x)
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    {
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        write(x);
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        push('\n');
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    }
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    struct AutoFlush
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    {
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        ~AutoFlush() { flush(); }
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    } _auto_flush;
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}
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using namespace FastIO;
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int main()
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{
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    int a, b;
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    // 读入第一个整数
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    if (read(a))
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    {
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        writeln(a);
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    }
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    else
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    {
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        // 文件为空或读取失败
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        return 0;
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    }
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    // 继续读入第二个
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    if (read(b))
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    {
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        writeln(b);
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    }
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    // 示例：循环读取所有整数直到 EOF
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    int x;
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    while (read(x))
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    {
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        writeln(x);
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    }
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    // 程序结束时自动刷新输出缓冲区
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    return 0;
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}