Read N Characters Given Read4_read n characters with read4-优快云博客

本文链接：https://blog.youkuaiyun.com/sundawei2016/article/details/77258855

本文介绍了一种利用read4 API实现read函数的方法，该函数可以从文件中读取指定数量的字符。通过两次循环和临时缓冲区的方式确保了正确处理文件末尾的情况，并能应对多次调用的需求。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

The API: int read4(char *buf) reads 4 characters at a time from a file.

The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.

By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.

Note:
The read function will only be called once for each test case.

API read4 返回所读字符的长度，可能是4，也可能比4小。调用read4 API 时需要传入char数组且长度为4.

read函数返回所读字符的长度，也许是n，也许比n 小

public int read(char[] buf, int n) {
        int cnt = 0;
        char[] tmp = new char[4];
        while (cnt < n) {
            int len = read4(tmp);
            if (len == 0) break;
            int idx = 0;
            while (cnt < n && idx < len) buf[cnt++] = tmp[idx++];
        }
        return cnt;
    }

The API: int read4(char *buf) reads 4 characters at a time from a file.

The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.

By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.

Note:
The read function may be called multiple times.

注意： read 函数可以被调用多次

因为要被调用多次，每次 tmp_ptr 到达 len 的长度时要被清零。

    char[] tmp = new char[4];
    int tmp_ptr = 0;
    int len = 0;
    public int read(char[] buf, int n) {
        int ptr = 0;
        while (ptr < n) {
            if (tmp_ptr == 0) {
                len = read4(tmp);
            }
            if (len == 0) break;
            while (ptr < n && tmp_ptr < len) {
                buf[ptr++] = tmp[tmp_ptr++];
            }
            if (tmp_ptr == len) tmp_ptr = 0;
        }
        return ptr;
    }