Read N Characters Given Read4算法详解

使用read4实现readN

最新推荐文章于 2019-03-08 22:21:23 发布

原创最新推荐文章于 2019-03-08 22:21:23 发布 · 691 阅读

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本文介绍了一种利用仅能一次读取四个字符的API来实现可以读取任意指定数量字符的功能。通过循环调用read4，并将读取的数据复制到目标缓冲区，直到达到所需的字符数或文件结束。

算法题目：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.

大致意思：用一个只读取4个字符的API，实现一个读取n个字符的API

int read4(char[] buf);
int read(char* buf, int n)
{
    char* buffer=new char[4];
    int readBytes=0;
    bool eof=false;
    while(!eof&&readBytes<n)
    {
        int lsize=read4(buffer);
        if(lsize<4)eof=true;
        if((readBytes+lsize)>n)
        {
            memcpy(buf+readBytes,buffer,n-readBytes);
            readBytes=n;
        }
        else
        {
            memcpy(buf+readBytes,buffer,lsize);
            readBytes+=lsize;
        }
    }
    return readBytes;
}