Question

你好我正在写一个简短的程序来实现一个shell，我遇到了一个不寻常的问题。由于某种原因，我无法清除std :: cout缓冲区。该程序不会打印出消息。我理解一个简单的解决方案是切换到std :: cerr，但有没有办法用cout打印消息？我尝试过的事情：

std::cout.flush()
在将任何内容写入标准输出后插入std::endl。
将std::flush插入输出流
std::cout.setf(std::ios::unitbuf);我发现这应该是非缓冲输出。

我非常感谢任何帮助，我的代码是：

int main()
{
    //Tryed this to unbuffer cout, no luck.
    std::cout.setf(std::ios::unitbuf);

    std::string input;

    //Print out shell prompt and read in input from keyboard.
    std::cout << "myshell> ";   
    std::getline(std::cin, input);

    //**********************************************************************
    //Step 1) Read in string and parse into tokens.
    //**********************************************************************

    char * buf = new char[input.length() + 1];
    strcpy(buf, input.c_str());

    int index = 0;
    char * command[256]; 

    command[index] = std::strtok(buf, " ");    //Get first token.
    std::cout << command[index] << std::endl;

    while (command[index] != NULL)
    {
        ++index;
        command[index] = std::strtok(NULL," ");    //Get remaining tokens.
        std::cout << command[index] << std::endl;
    }   

    std::cout.flush(); //No luck here either

    //HERE IS WHERE MY PROBLEM IS.
    std::cout << index << " items were added to the command array" << std::endl;

    delete[] buf;

    return 0;   
}

Answer 1

问题是，您在NULL循环的最后一次迭代中向cout发送了while，这导致了UB，并且在您的情况下正在干扰{{1} }。在向cout发送任何内容之前检查NULL，您没问题：

cout

Answer 2

如果您需要知道您的信息流发生了什么，请记住他们可以携带状态信息（the iostate, which I recommend you read about）。以下代码可能有助于跟踪您的错误：

 try {
      std::cout.exceptions(std::cout.failbit);          
 } catch(const std::ios_base::failure& e) {
      std::cerr << "stream error: " << e.what() << std::endl;
      std::cout.clear();
 }

 // continue working with cout, because std::cout.clear() removed
 // failbit

或者，甚至更简单：

if(not std::cout) {
    // address your error (if it is recoverable)
 }

这就是您的代码的样子：

#include <cstring>
#include <string>
#include <iostream>
int main()
{
    //Tryed this to unbuffer cout, no luck.
    std::cout.setf(std::ios::unitbuf);

    std::string input;

    //Print out shell prompt and read in input from keyboard.
    std::cout << "myshell> ";   
    std::getline(std::cin, input);

    //**********************************************************************
    //Step 1) Read in string and parse into tokens.
    //**********************************************************************

    char * buf = new char[input.length() + 1];
    strcpy(buf, input.c_str());

    int index = 0;
    char * command[256]; 

    command[index] = std::strtok(buf, " ");    //Get first token.
    std::cout << command[index] << std::endl;

    while (command[index] != NULL)
    {
        ++index;
        command[index] = std::strtok(NULL," ");    //Get remaining tokens.
        std::cout << command[index] << std::endl;
    }

    // I added from here...
    if(not std::cout) {
      std::cerr << "cout is messed up... fixing it..." << std::endl;
      std::cout.clear();
    }
    // ... to here.

    std::cout.flush(); //No luck here either

    //HERE IS WHERE MY PROBLEM IS.
    std::cout << index << " items were added to the command array" << std::endl;

    delete[] buf;

    return 0;   
}

结果：

$ ./a.out
myshell> 1 2 3
1
2
3
cout is messed up... fixing it...
3 items were added to the command array

清除cout缓冲区（c ++）

2 个答案: