157 Read N Characters Given Read4

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.

// Forward declaration of the read4 API.
int read4(char *buf);

class Solution {
public:
    /**
     * @param buf Destination buffer
     * @param n   Maximum number of characters to read
     * @return    The number of characters read
     */
    int read(char *buf, int n) {
        int res = 0;
        int read_char = 0;
        while (res<n)
        {
            read_char = read4(buf+res);
            res += read_char;
            if (read_char<4)
                break;
        }
        if (res>=n)
        {
            buf[n]='\0';
            res = n;
        }
        return res;
    }
};