c++ - Boost::iostreams::filtering_istreams 等待 E.O.F

Question

我将使用 filtering_istream 作为 std::cin 的包装器。但它没有像我预期的那样工作。它正在等待 E.O.F请帮助我理解这种行为。

#include <iostream>
#include <boost/iostreams/filtering_stream.hpp>
// compile using g++ -std=c++11 -lboost_iostreams

int main(){
    boost::iostreams::filtering_istream cinn(std::cin);
    std::cout << "Write something:";

    char c;
    while(true){
        cinn.get(c);
        std::cout << "Your character is : " << c << "\n";
        if(c=='.') break;
    }
}

我希望它的工作方式类似于这段代码。

#include <iostream>
#include <boost/iostreams/filtering_stream.hpp>

int main(){
    //boost::iostreams::filtering_istream cinn(std::cin);
    std::cout << "Write something:";

    char c;
    while(true){
        std::cin.get(c);
        std::cout << "Your character is : " << c << "\n";
        if(c=='.') break;
    }
}

代码1的输出是

$./a.out
hello
how.are_you
Write something:Your character is : h
Your character is : e
Your character is : l
Your character is : l
Your character is : o
Your character is : 

Your character is : h
Your character is : o
Your character is : w
Your character is : .

代码2的输出是

$./a.out
Write something:hello
Your character is : h
Your character is : e
Your character is : l
Your character is : l
Your character is : o
Your character is : 

how.are_you
Your character is : h
Your character is : o
Your character is : w
Your character is : .

代码 2 给出了我预期的输出。它读取每一行并对其进行处理。而 Code1 读取所有行直到它得到 E.O.F。然后打印输出。

两种代码的行为不同。我无法理解这种行为。请帮忙。提前致谢。

Answer 1

您正在查看缓冲。缓冲发生在许多级别。在这种情况下，您可能正在查看过滤流中的缓冲。

你可以玩一些类似的东西

• 设置设备缓冲区大小
• 设置过滤器缓冲区大小
• 设置_pback_buffer_size

在我的机器上，我使用 ( docs) 得到了你想要的结果

boost::iostreams::filtering_istream cinn(std::cin, 0, 1);