逐字节读取二进制istream [英] Reading binary istream byte by byte

问题描述

我试图使用ifstream逐字节读取二进制文件.我之前曾使用过像get()这样的istream方法来一次读取二进制文件的整个块，而不会出现问题.但是我当前的任务是使自己逐字节运行，并依靠io系统中的缓冲来使其高效.问题在于，我似乎比原先快了几个字节到达文件末尾.因此，我编写了以下测试程序:

I was attempting to read a binary file byte by byte using an ifstream. I've used istream methods like get() before to read entire chunks of a binary file at once without a problem. But my current task lends itself to going byte by byte and relying on the buffering in the io-system to make it efficient. The problem is that I seemed to reach the end of the file several bytes sooner than I should. So I wrote the following test program:

#include <iostream>
#include <fstream>

int main() {
    typedef unsigned char uint8;
    std::ifstream source("test.dat", std::ios_base::binary);
    while (source) {
        std::ios::pos_type before = source.tellg();
        uint8 x;
        source >> x;
        std::ios::pos_type after = source.tellg();
        std::cout << before << ' ' << static_cast<int>(x) << ' '
                  << after << std::endl;
    }
    return 0;
}

这将转储test.dat的内容，每行一个字节，显示文件前后的位置.

This dumps the contents of test.dat, one byte per line, showing the file position before and after.

果然，如果我的文件碰巧有两个字节的序列0x0D-0x0A(对应于回车和换行)，则这些字节将被跳过.

Sure enough, if my file happens to have the two-byte sequence 0x0D-0x0A (which corresponds to carriage return and line feed), those bytes are skipped.

• 我已经以二进制模式打开了流.那不应该阻止它解释行分隔符吗?
• 提取运算符是否总是使用文本模式?
• 从二进制istream逐字节读取字节的正确方法是什么?

Windows上的MSVC ++ 2008.

MSVC++ 2008 on Windows.

推荐答案

>>提取器用于格式化输入；他们跳过空格(由 默认).对于单字符无格式输入，可以使用 istream::get() (返回int，如果读取的是EOF失败，或者 [0，UCHAR_MAX]范围内的值)或istream::get(char&)(将 在参数中读取的字符，返回转换为 bool，如果读取成功，则为true，如果读取失败，则为false.

The >> extractors are for formatted input; they skip white space (by default). For single character unformatted input, you can use istream::get() (returns an int, either EOF if the read fails, or a value in the range [0,UCHAR_MAX]) or istream::get(char&) (puts the character read in the argument, returns something which converts to bool, true if the read succeeds, and false if it fails.

这篇关于逐字节读取二进制istream的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！