I/O流字符串操作(正确的Cin/cout运算符<</>)) [英] I/O Stream String Manipulation (Correct Cin/cout operators <</>>)

问题描述

我遇到了这个问题在这里，还对答案给出了另一个问题(由于我是stackoverflow的新手，所以我无法发表评论).回答这个问题的人似乎对替换<< >>用于cin和cout.但是我遇到的问题是所有分号都不会显示在新的输出文件中.

I came across this question on here and had a further question about the answer give (I can't comment since I'm new to stackoverflow). The guy who answered it seems to be right about replacing << >> for cin and cout. But the problem I'm having is that all the semi-colons won't show up in the new output file.

我知道 while std::getline(input, command, ';') 会擦除所有分号，但是应该在末尾将它们与else语句放回去，但是在我运行它时不会被替换.如果我省略';'在getline语句之外，输出文件中的所有内容都混乱了.

I know that while std::getline(input, command, ';') erases all semicolons, but theyre supposed to be put back with the else statement at the end, but it isn't being replaced when I run it. And if I omit ';' out of the getline statement everything in the output file messes up.

如何显示分号呢?

void print(ifstream& input,ofstream& output)
{
    bool first = true;
    std::string command;
    while(std::getline(input, command, ';'))
    { // loop until no more input to read or input fails to be read
        if (command.find("cin")!= std::string::npos)
        { // found cin somewhere in command. This is too crude to work. See below
            size_t pos = command.find("<<"); // look for the first <<
            while (pos != std::string::npos)
            { // keep replacing and looking until end of string
                command.replace(pos, 2, ">>"); // replace with >>
                pos = command.find("<<", pos); // look for another 
            }
        }
        else if (command.find("cout")!= std::string::npos)
        { // same as above, but other way around
            size_t pos = command.find(">>"); 
            while (pos != std::string::npos)
            {
                command.replace(pos, 2, "<<");
                pos = command.find(">>", pos);
            }
        }
        if (! first)
        {
            output << command; // write string to output
        }
        else
        {
            first = false;
            output << ';' << command; // write string to output
        }
    }
}

推荐答案

问题在这里:

        if (! first)
        {
            output << command; // write string to output
        }
        else
        {
            first = false;
            output << ';' << command; // write string to output
        }

在第一次迭代中，执行else分支并打印分号.

In the first iteration, the else branch gets executed and a semicolon is printed.

在以后的任何迭代中，将执行if分支，这不会不打印分号.

In any later iteration, the if branch is executed, which does not print a semicolon.

修复很容易:交换以output <<开头的两行.

The fix is easy: Swap the two lines starting with output <<.

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